Photomask, pattern formation method using photomask and mask data creation method

ABSTRACT

A mask pattern includes a main pattern to be transferred through exposure and an auxiliary pattern that diffracts exposing light and is not transferred through the exposure. The main pattern is made from a shielding portion, a phase shifter or a combination of a semi-shielding portion or a shielding portion and a phase shifter. The auxiliary pattern is made from a shielding portion or a semi-shielding portion. The auxiliary pattern is disposed in a position away from the main pattern by a distance M×(λ/(2×sin φ)) or M×((λ/(2×sin φ))+(λ/(NA+sin φ))), wherein λ indicates a wavelength of the exposing light, M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner and φ indicates an oblique incident angle.

RELATED APPLICATION:

This application is a divisional application of Ser. No. 10/717,598,filed Nov. 21, 2003, which claims priority of Japanese Patentapplication No. 2003-037845, filed Feb. 17, 2003, and the contents ofwhich are herewith incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a photomask used for forming a finepattern in fabrication of semiconductor integrated circuit devices and apattern formation method using the photomask, and further relates to adesign method for a mask pattern.

Recently, there are increasing demands for refinement of circuitpatterns in order to increase the degree of integration of a large scaleintegrated circuit (hereinafter referred to as the LSI) realized byusing semiconductors. As a result, thinning of an interconnect patternused for forming a circuit has become very significant.

Now, conventional thinning of an interconnect pattern using an opticalexposure system will be described by exemplifying use of positive resistprocess. Herein, a line pattern means a portion of a resist film notexposed to exposing light, that is, a resist portion remaining afterdevelopment (namely, a resist pattern). Also, a space pattern is aportion of the resist film exposed to the exposing light, that is, anopening where the resist film is removed through the development(namely, a resist removal pattern). In the case where negative resistprocess is employed instead of the positive resist process, theabove-described definitions of a line pattern and a space pattern arereplaced with each other.

Conventionally, in the case where pattern formation is carried out byusing an optical exposure system, a photomask in which a completelyshielding pattern of Cr or the like is drawn correspondingly to adesired pattern on a transparent substrate of quartz or the like isused. In such a photomask, an area where the Cr pattern is present worksas a shielding portion that does not transmit exposing light of a givenwavelength at all (namely, that has transmittance of substantially 0%),and an area where the Cr pattern is not present (an opening) works as atransparent portion that has transmittance equivalent to that of thetransparent substrate against the exposing light (namely, that hastransmittance of substantially 100%). When this photomask is used forthe exposure, the shielding portion corresponds to an unexposed portionof a resist and the opening (transparent portion) corresponds to anexposed portion of the resist. Accordingly, such a photomask, namely, aphotomask consisting of a shielding portion and a transparent portionagainst exposing light of a given wavelength, is designated as a binarymask.

In an optical exposure system, an image formed through exposure usingthe above-described binary mask (namely, an energy intensitydistribution caused on a target material through the exposure) hascontrast in inverse proportion to λ/NA, wherein λ indicates thewavelength of the exposing light emitted from a light source and NAindicates numerical aperture of a reducing projection optical system(specifically, a projection lens) of an aligner. Therefore, a dimensionthat can be formed as a resist pattern is in proportion to λ/NA.Accordingly, in order to realize refinement of a pattern, it iseffective to reduce the wavelength λ of the exposing light and increasethe numerical aperture NA.

On the other hand, for example, since steps are caused in formation ofdevices included in an LSI or the surface of a substrate is not flat, animage formed by using the conventional optical exposure system may beshifted from an ideal focal point. Therefore, the dimension of a patternformed in such a defocused state should be kept in a predeterminedrange. The limit of a defocus value at which the dimension of a patternfalls within the predetermined range, namely, the limit of a defocusvalue for securing the dimensional accuracy of a pattern, is designatedas a depth of focus (DOF). Specifically, in order to refine a pattern,it is necessary not only to emphasize the contrast of an image but alsoto increase the value of a DOF. The DOF value is, however, in proportionto λ/NA², and therefore, when the wavelength is reduced and thenumerical aperture NA is increased for improving the contrast, the DOFvalue is unavoidably reduced.

As described so far, a technique to simultaneously realize improvementof contrast by a method other than by reducing the wavelength andincreasing the numerical aperture and improvement of a DOF withoutchanging the wavelength λ and the numerical aperture NA has becomesignificant.

In the most typical method for largely improving the contrast and theDOF, oblique incident exposure (off-axis illumination) is performed onperiodical patterns provided on a photomask. However, the obliqueincident exposure can exhibit a satisfactory effect merely when thepatterns are arranged at a small period of λ/NA or less, and hence isnot an effective method for refinement of arbitrary patterns. In orderto make up for this weak point of the oblique incident exposure, thereis a method using an auxiliary pattern (hereinafter referred to as theauxiliary pattern method).

Now, an auxiliary pattern method disclosed in Japanese Laid-Open PatentPublication No. 5-165194 (hereinafter referred to as the firstconventional example) will be described. FIG. 35 is a plan view of aphotomask used in the first conventional example. The photomask of FIG.35 is used in a stepper for performing ⅕ reduction projection exposure.As shown in FIG. 35, a shielding film 11 of chromium is provided on atransparent glass substrate 10 working as a mask substrate. A firstopening 12 corresponding to a main pattern (circuit pattern) to betransferred through the exposure is formed in the shielding film 11.Also, a pair of second openings 13 that correspond to an auxiliarypattern for improving the transfer accuracy of the main pattern and arenot transferred through the exposure are provided in the shielding film11 on both sides of the first opening 12. In this case, the firstopening 12 has a width of, for example, 1.5 μm and each second opening13 has a width of, for example, 0.75 μm. Also, the distance between thecenter of the first opening 12 and the center of each second opening 13is, for example, 4.5 μm. In other words, in the photomask used in thefirst conventional example, an auxiliary pattern smaller than a circuitpattern, namely, a main pattern, is provided to be adjacent to thecircuit pattern. In the auxiliary pattern method of the firstconventional example, although the DOF is slightly improved, the effectequivalent to that attained by using the original periodic patternscannot be attained.

Next, an auxiliary pattern method disclosed in Japanese Laid-Open PatentPublication No. 9-73166 (hereinafter referred to as a secondconventional example), which is obtained by improving the firstconventional example, will be described. FIG. 36 is a plan view of aphotomask used in the second conventional example. As shown in FIG. 36,a main pattern 21 is provided on a transparent glass substrate 20working as a mask substrate, and auxiliary patterns 22 are periodicallyarranged on the glass substrate 20 on both sides of the main pattern 21.The main pattern 21 is made from a multilayer film consisting of a lowerlow transmittance film and an upper shielding film (chromium film). Eachauxiliary pattern 22 is made from the low transmittance film obtained byremoving the upper shielding film from the multilayer film. At thispoint, the auxiliary pattern 22 made from the low transmittance film isnot used for forming an unexposed portion of a resist (i.e., a resistpattern) through exposure. Accordingly, when the oblique incidentexposure is performed with the auxiliary patterns 22 having lowtransmittance periodically arranged against the main pattern 21, the DOFcan be improved.

Although the contrast and the DOF can be largely improved by using aphase shifter, but this effect can be attained merely in the case wherea transparent portion (opening) and a phase shifter for transmittingexposing light at a phase difference of 180° with respect to thetransparent portion can be arranged on both sides of a fine line patternon a photomask. Accordingly, even when a phase shifter is used, thecontrast and the DOF cannot be improved all over fine portions of aninterconnect pattern of a general LSI.

Also, the contrast and the DOF can be largely improved in a completelyperiodic pattern by using the oblique incident exposure. However, thiseffect cannot be attained all over fine portions of an interconnectpattern including an isolated pattern of a general LSI. In this case,the DOF and the like can be slightly improved by using an auxiliarypattern (as in the first conventional example), but the effect is slightas compared with that attained in a completely periodic patterns. Also,when a pattern having low transmittance is used as an auxiliary patternso as to improve the degree of freedom in the arrangement of theauxiliary pattern, the periodicity in the arrangement of patterns can beimproved (as in the second conventional example). Also in this case,however, there arises the following problem: a substantial effectattained by the second conventional example is merely to ease processingof the auxiliary patterns because the auxiliary patterns can be madethick. In other words, with respect to the improvement of the contrastand the DOF, the second conventional example can attain the effectmerely equivalent to that attained by the first conventional example(using a thin auxiliary pattern). This is because the improvement of thecontrast and the DOF does not depend upon whether a mask patternconsisting of a main pattern and an auxiliary pattern is periodic butdepends upon whether an image formed by using a mask pattern throughexposure (i.e., an energy intensity distribution) is highly periodic.

SUMMARY OF THE INVENTION

In consideration of the above-described conventional problems, an objectof the invention is providing a photomask, a pattern formation methodand a method for creating mask data that can improve contrast and a DOFin forming a pattern in an arbitrary shape.

In order to achieve the object, the first photomask of the inventionincludes a mask pattern formed on a transparent substrate; and atransparent portion of the transparent substrate where the mask patternis not formed. Specifically, the mask pattern includes a main pattern tobe transferred through exposure and an auxiliary pattern that diffractsexposing light and is not transferred through the exposure. Also, themain pattern is composed of a first semi-shielding portion that hasfirst transmittance for partially transmitting the exposing light andtransmits the exposing light in an identical phase with respect to thetransparent portion, and a phase shifter that transmits the exposinglight in an opposite phase with respect to the transparent portion.Furthermore, the auxiliary pattern is made from a second semi-shieldingportion that has second transmittance for partially transmitting theexposing light and transmits the exposing light in the identical phasewith respect to the transparent portion.

Herein, the identical phase means that a phase difference is not lessthan (−30+360×n) degrees and not more than (30+360×n) degrees (wherein nis an integer), and the opposite phase means that a phase difference isnot less than (150+360×n) degrees and not more than (210+360×n) degrees(wherein n is an integer).

In the first photomask, since the main pattern is composed of thesemi-shielding portion and the phase shifter, lights passing through thetransparent portion and the semi-shielding portion can be partiallycancelled by light passing through the phase shifter. Therefore, thecontrast in a light intensity distribution of a shielded imagecorresponding to the main pattern can be emphasized. Also, since theauxiliary pattern with low transmittance is provided separately from themain pattern, when the auxiliary pattern is disposed in an appropriateposition, diffraction light for interfering with the light passingthrough the phase shifter of the main pattern can be generated.Accordingly, the defocus characteristic of a transferred image of themain pattern can be improved, resulting in improving the DOFcharacteristic.

Furthermore, in the first photomask, since the auxiliary pattern is madefrom the semi-shielding portion, the degree of freedom in thearrangement of the auxiliary pattern can be improved, and hence, theperiodicity in the arrangement of the patterns including the mainpattern can be improved, so that the DOF characteristic can be furtherimproved. Also, since the auxiliary pattern is made from thesemi-shielding portion, it can be made thick under restriction that itis not transferred through the exposure, and hence it can be easilyprocessed.

In the first photomask, the first transmittance is preferably 15% orless.

Thus, the thickness of a resist film can be prevented from reducing orthe resist sensitivity can be optimized in the pattern formation.Specifically, such an effect and the effects to improve the DOF and thecontrast can be both attained.

In the first photomask, the second transmittance is preferably not lessthan 6% and not more than 50%.

Thus, the effect to improve the DOF derived from the diffraction lightcan be definitely realized while preventing an unexposed portion frombeing formed in a resist due to a too high shielding property of theauxiliary pattern.

The second photomask of this invention includes a mask pattern formed ona transparent substrate; and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the maskpattern includes a main pattern to be transferred through exposure andan auxiliary pattern that diffracts exposing light and is nottransferred through the exposure. Furthermore, a part of the transparentportion is disposed between the main pattern and the auxiliary pattern,and with respect to an oblique incident angle φA defined as sin φA=NA×SAwhen a given oblique incident position is indicated by SA (wherein0.4≦SA≦0.8), a center of the auxiliary pattern is disposed in or in thevicinity of a position away from a center of the main pattern by adistance M×(λ/2×sin φA)), wherein λ indicates a wavelength of theexposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.

In the second photomask, the. auxiliary pattern is provided separatelyfrom the main pattern in or in the vicinity of a position away from themain pattern by a distance M×(λ/2×sin φA)). Therefore, the defocuscharacteristic of a transferred image of the main pattern can beimproved owing to diffraction light generated by the auxiliary pattern,resulting in improving the DOF characteristic.

In the second photomask, the main pattern may be made from a shieldingportion or a phase shifter that transmits the exposing light in anopposite phase with respect to the transparent portion.

In the second photomask, the main pattern is preferably composed of asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion, and a phase shifter thattransmits the exposing light in an opposite phase with respect to thetransparent portion.

Thus, since the main pattern is composed of the semi-shielding portionand the phase shifter, lights passing through the transparent portionand the semi-shielding portion can be partially cancelled by lightpassing through the phase shifter. Therefore, the contrast in a lightintensity distribution of a shielded image corresponding to the mainpattern can be emphasized.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedat a center of the main pattern to be surrounded by the semi-shieldingportion.

Thus, the contrast in the light intensity distribution can be emphasizedat the center of the shielded image corresponding to the main pattern,and therefore, while keeping a good defocus characteristic, for example,a fine line pattern can be formed. Furthermore, a dimension of a part ofthe semi-shielding portion sandwiched between the phase shifter and thetransparent portion is preferably not less than 20 nm and not more than(0.3×λ/NA)×M, or not less than ¼ of a wavelength of the exposing lightand not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of theexposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.Alternatively, the main pattern may be composed of a shielding portionreplaced with the semi-shielding portion and the phase shifter.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedin a peripheral portion of the main pattern to be surrounded by a partof the semi-shielding portion.

Thus, the contrast in the light intensity distribution can be emphasizedin the vicinity of the main pattern in an image of light having passedthrough the transparent portion. Therefore, while keeping a good defocuscharacteristic, for example, a fine contact pattern can be formed.

Furthermore, in the case where the main pattern is composed of thesemi-shielding portion and the phase shifter, the semi-shielding portionpreferably has transmittance of 15% or less.

Thus, the thickness of a resist film can be prevented from reducing orthe resist sensitivity can be optimized in the pattern formation.Specifically, such an effect and the effects to improve the DOF and thecontrast can be both attained.

In the second photomask, the auxiliary pattern may be made from ashielding portion or a semi-shielding portion that has transmittance forpartially transmitting the exposing light and transmits the exposinglight in an identical phase with respect to the transparent portion.When the auxiliary pattern is made from the semi-shielding portion, thedegree of freedom in the arrangement of the auxiliary pattern can beimproved, and hence, the periodicity in the arrangement of the patternsincluding the main pattern can be improved, so that the DOFcharacteristic can be further improved. Furthermore, when the auxiliarypattern is made from the semi-shielding portion, the auxiliary patterncan be made thick under restriction that it is not transferred throughthe exposure, and hence, the auxiliary pattern can be easily processed.In the case where the auxiliary pattern is made from the semi-shieldingportion, the transmittance of the semi-shielding portion is preferablynot less than 6% and not more than 50%. Thus, the effect to improve theDOF derived from the diffraction light can be definitely realized whilepreventing an unexposed portion from being formed in a resist due to atoo high shielding property of the auxiliary pattern.

The third photomask of the invention includes a mask pattern formed on atransparent substrate; and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the maskpattern includes a main pattern to be transferred through exposure andan auxiliary pattern that diffracts exposing light and is nottransferred through the exposure. Furthermore, a part of the transparentportion is disposed between the main pattern and the auxiliary pattern,and with respect to an oblique incident angle φB defined as sin φB=NA×SBwhen a given oblique incident position is indicated by SB (0.4≦SB≦0.8),a center of the auxiliary pattern is disposed in or in the vicinity of aposition away from a center of the main pattern by a distanceM×((λ/(2×sin φB))+(λ/(NA+sin φB)), wherein λ indicates a wavelength ofthe exposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.

In the third photomask, the auxiliary pattern is provided separatelyfrom the main pattern in or in the vicinity of a position away from themain pattern by a distance M×((λ/(2×sin φB))+(λ/(NA+sin φB)). Therefore,the defocus characteristic of a transferred image of the main patterncan be improved owing to diffraction light generated by the auxiliarypattern, resulting in improving the DOF characteristic. Furthermore,when a first auxiliary pattern is disposed in or in the vicinity of aposition away from the main pattern by a distance M×(λ/(2×sin φB)) and asecond auxiliary pattern is disposed in or in the vicinity of a positionaway from the main pattern by a distance M×((λ/(2×sin φB))+(λ/(NA+sinφB)), the following effect can be attained: Since the first auxiliarypattern functions as a first-order diffraction light generation patternand the second auxiliary pattern functions as a second-order diffractionlight generation pattern, the effect to improve the DOF can be furtherincreased.

In the third photomask, the main pattern may be made from a shieldingportion or a phase shifter that transmits the exposing light in anopposite phase with respect to the transparent portion.

In the third photomask, the main pattern is preferably composed of asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion, and a phase shifter thattransmits the exposing light in an opposite phase with respect to thetransparent portion.

Thus, since the main pattern is composed of the semi-shielding portionand the phase shifter, lights passing through the transparent portionand the semi-shielding portion can be partially cancelled by lightpassing through the phase shifter. Therefore, the contrast in the lightintensity distribution in a shielded image corresponding to the mainpattern can be emphasized.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedat a center of the main pattern to be surrounded by the semi-shieldingportion.

Thus, the contrast in the light intensity distribution can be emphasizedat the center of the shielded image corresponding to the main pattern,and therefore, while keeping a good defocus characteristic, for example,a fine line pattern can be formed. Also, a dimension of a part of thesemi-shielding portion sandwiched between the phase shifter and thetransparent portion is preferably not less than 20 nm and not more than(0.3×λ/NA)×M, or not less than ¼ of a wavelength of the exposing lightand not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of theexposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.Alternatively, the main pattern may be composed of a shielding portionreplaced with the semi-shielding portion and the phase shifter.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedin a peripheral portion of the main pattern to be surrounded by a partof the semi-shielding portion.

Thus, the contrast in the light intensity distribution can be emphasizedin the vicinity of the main pattern in an image formed by light havingpassed through the transparent portion, and hence, while keeping a gooddefocus characteristic, for example, a fine contact pattern can beformed.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the semi-shielding portion preferably hastransmittance of 15% or less.

Thus, the thickness of a resist film can be prevented from reducing orthe resist sensitivity can be optimized in the pattern formation.Specifically, such an effect and the effects to improve the DOF and thecontrast can be both attained.

In the third photomask, the auxiliary pattern may be made from ashielding portion or a semi-shielding portion that has transmittance forpartially transmitting the exposing light and transmits the exposinglight in an identical phase with respect to the transparent portion.When the auxiliary pattern is made from the semi-shielding portion, thedegree of freedom in the arrangement of the auxiliary pattern can beimproved, and hence, the periodicity in the arrangement of the patternsincluding the main pattern can be improved, so that the DOFcharacteristic can be further improved. Also, when the auxiliary patternis made from the semi-shielding portion, the auxiliary pattern can bemade thick under restriction that it is not transferred through theexposure, and hence, the auxiliary pattern can be easily processed. Inthe case where the auxiliary pattern is made from the semi-shieldingportion, the transmittance of the semi-shielding portion is preferablynot less than 6% and not more than 50%. Thus, the effect to improve theDOF derived from the diffraction light can be definitely realized whilepreventing an unexposed portion from being formed in a resist due to atoo high shielding property of the auxiliary pattern.

In the second or third photomask, in the case where the auxiliarypattern is disposed in a position away from the phase shifter by adistance M×(λ/(2×sin φ)) or M×((λ/(2×sin φ))+(λ/(NA+sin φ)), the obliqueincident angle φ is preferably not less than φ1 and not more than φ2 orsatisfies ((φ1+φ2)/2 or (ξ+φ2)/2, wherein φ1 and φ2 indicate the minimumoblique incident angle and the maximum oblique incident angle of anoblique incident illumination system of the aligner and ξ indicates anangle satisfying sin ξ=0.4×NA, wherein NA is numerical aperture of thereduction projection optical system of the aligner.

The fourth photomask of this invention includes a mask pattern formed ona transparent substrate; and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the maskpattern includes a main pattern to be transferred through exposure andan auxiliary pattern that diffracts exposing light and is nottransferred through the exposure. Furthermore, the auxiliary patternincludes a first auxiliary pattern that is disposed in or in thevicinity of a position away from a center of the main pattern by adistance X with a part of the transparent portion sandwiched between themain pattern and the first auxiliary pattern, and a second auxiliarypattern that is disposed on a side of the first auxiliary patternfarther from the main pattern in or in the vicinity of a position awayfrom a center of the first auxiliary pattern by a distance Y with a partof the transparent portion sandwiched between the first auxiliarypattern and the second auxiliary pattern. In this case, the distance Xis larger than the distance Y.

Herein, a distance between the main pattern and the auxiliary patternmeans a distance between the centers thereof. For example, in the casewhere an auxiliary pattern in an analogous shape is provided in parallelto a line-shaped main pattern, the distance means a distance between thecenter lines of the main pattern and the auxiliary pattern.

In the fourth photomask, the first auxiliary pattern is providedseparately from the main pattern in or in the vicinity of the positionaway from the main pattern by the distance X, and the second auxiliarypattern is provided in or in the vicinity of the position away from thefirst auxiliary pattern by the distance Y smaller than the distance X.Therefore, the defocus characteristic of a transferred image of the mainpattern can be improved by diffraction light generated by each auxiliarypattern, resulting in improving the DOF characteristic.

In the fourth photomask, when a given oblique incident position isindicated by S (wherein 0.4≦S≦0.8), a relationship, X/Y=(1+S)/(2×S),preferably holds. Thus, the effect to improve the DOF can be maximized.

In the fourth photomask, when a given oblique incident position isindicated by SA (wherein 0.4≦SA≦0.8), with respect to an obliqueincident angle φA defined as sin φA=NA×SA, a relationship, X=M×(λ/(2×sinφA), may hold.

In the fourth photomask, the main pattern may be made from a shieldingportion or a phase shifter that transmits the exposing light in anopposite phase with respect to the transparent portion.

In the fourth photomask, the main pattern is preferably composed of asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion, and a phase shifter thattransmits the exposing light in an opposite phase with respect to thetransparent portion.

Thus, since the main pattern is composed of the semi-shielding portionand the phase shifter, lights passing through the transparent portionand the semi-shielding portion can be partially canceled by lightpassing through the phase shifter. Therefore, the contrast in a lightintensity distribution of a shielded image corresponding to the mainpattern can be emphasized.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedat a center of the main pattern to be surrounded by the semi-shieldingportion.

Thus, the contrast in the light intensity distribution can be emphasizedat the center of the shielded image corresponding to the main pattern,and hence, while keeping a good defocus characteristic, for example, afine line pattern can be formed. Furthermore, a dimension of a part ofthe semi-shielding portion sandwiched between the phase shifter and thetransparent portion is not less than 20 nm and not more than(0.3×λ/NA)×M, or not less than ¼ of a wavelength of the exposing lightand not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of theexposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.Alternatively, the main pattern may be composed of a shielding portionreplaced with the semi-shielding portion and the phase shifter.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedin a peripheral portion of the main pattern to be surrounded by a partof the semi-shielding portion.

Thus, the contrast in the light intensity distribution can be emphasizedin the vicinity of the main pattern in an image formed by light havingpassed through the transparent portion. Therefore, while keeping a gooddefocus characteristic, for example, a fine contact pattern can beformed.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the semi-shielding portion preferably hastransmittance of 15% or less.

Thus, the thickness of a resist film can be prevented from reducing orthe resist sensitivity can be optimized in the pattern exposure.Specifically, such an effect and the effects to improve the DOF and thecontrast can be both attained.

In the fourth photomask, the first auxiliary pattern and the secondauxiliary pattern may be made from a shielding portion or asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion. When each auxiliarypattern is made from the semi-shielding portion, the degree of freedomin the arrangement of the auxiliary patterns can be improved, and hence,the periodicity in the arrangement of the patterns including the mainpattern can be improved, so that the DOF characteristic can be furtherimproved. Also, when the auxiliary patterns are made from thesemi-shielding portion, the auxiliary patterns can be made thick underrestriction that they are not transferred through the exposure, andhence, the auxiliary patterns can be easily processed. In the case wherethe auxiliary patterns are made from the semi-shielding portion, thetransmittance of the semi-shielding portion is preferably not less than6% and not more than 50%. Thus, the effect to improve the DOF derivedfrom the diffraction light can be definitely realized while preventingan unexposed portion from being formed in a resist due to a too highshielding property of the auxiliary patterns.

The fifth photomask of the invention includes a mask pattern formed on atransparent substrate; and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the maskpattern includes a main pattern to be transferred through exposure andan auxiliary pattern that diffracts exposing light and is nottransferred through the exposure. Furthermore, the auxiliary patternincludes a first auxiliary pattern that has a width D1 and is disposedwith a part of the transparent portion sandwiched between the mainpattern and the first auxiliary pattern and a second auxiliary patternthat has a width D2 and is disposed on a side of the first auxiliarypattern farther from the main pattern with a part of the transparentportion sandwiched between the first auxiliary pattern and the secondauxiliary pattern. In this case, the width D2 is larger than the widthD1.

In the fifth photomask, since the first and second auxiliary patternsare provided separately from the main pattern, the defocuscharacteristic of a transferred image of the main pattern can beimproved owing to diffraction light generated by each auxiliary pattern,resulting in improving the DOF characteristic. Also, since the width D2of the second auxiliary pattern farther from the main pattern is largerthan the width D1 of the first auxiliary pattern closer to the mainpattern, while keeping a large exposure margin, the effect to improvethe DOF can be attained.

In the fifth photomask, a ratio D2/D1 is preferably not less than 1.2and not more than 2. Thus, the effect to improve the DOF can be attainedwhile preventing an unexposed portion from being formed in a resist bythe auxiliary patterns.

In the fifth photomask, the main pattern may be made from a shieldingportion or a phase shifter that transmits the exposing light in anopposite phase with respect to the transparent portion.

In the fifth photomask, the main pattern is preferably composed of asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion, and a phase shifter thattransmits the exposing light in an opposite phase with respect to thetransparent portion.

Thus, since the main pattern is composed of the semi-shielding portionand the phase shifter, lights passing through the transparent portionand the semi-shielding portion can be partially cancelled by lightpassing through the phase shifter. Therefore, the contrast in a lightintensity distribution of a shielded image corresponding to the mainpattern can be emphasized.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedat a center of the main pattern to be surrounded by the semi-shieldingportion.

Thus, the contrast in the light intensity distribution can be emphasizedat the center of the shielded image corresponding to the main pattern,and hence, while keeping a good defocus characteristic, for example, afine line pattern can be formed. Furthermore, a dimension of a part ofthe semi-shielding portion sandwiched between the phase shifter and thetransparent portion is preferably not less than 20 nm and not more than(0.3×λ/NA)×M, or not less than ¼ of a wavelength of the exposing lightand not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of theexposing light and M and NA indicate magnification and numericalaperture of a reduction projection optical system of an aligner.Alternatively, the main pattern may be composed of a shielding portionreplaced with the semi-shielding portion and the phase shifter.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the phase shifter is preferably disposedin a peripheral portion of the main pattern to be surrounded by a partof the semi-shielding portion.

Thus, the contrast in the light intensity distribution can be emphasizedin the vicinity of the main pattern in an image formed by light havingpassed through the transparent portion. Therefore, while keeping a gooddefocus characteristic, for example, a fine contact pattern can beformed.

In the case where the main pattern is composed of the semi-shieldingportion and the phase shifter, the semi-shielding portion preferably hastransmittance of 15% or less.

Thus, the thickness of a resist film can be prevented from reducing orthe resist sensitivity can be optimized in the pattern formation.Specifically, such an effect and the effects to improve the DOF and thecontrast can be both attained.

In the fifth photomask, the first auxiliary pattern and the secondauxiliary pattern may be made from a shielding portion or asemi-shielding portion that has transmittance for partially transmittingthe exposing light and transmits the exposing light in an identicalphase with respect to the transparent portion. When each auxiliarypattern is made from the semi-shielding portion, the degree of freedomin the arrangement of the auxiliary patterns can be improved, and hence,the periodicity in the arrangement of the patterns including the mainpattern can be improved, so that the DOF characteristic can be furtherimproved. Also, when the auxiliary patterns are made from thesemi-shielding portion, the auxiliary patterns can be made thick underrestriction that they are not transferred through the exposure, andhence, the auxiliary patterns can be easily processed. In the case wherethe auxiliary patterns are made from the semi-shielding portion, thetransmittance of the semi-shielding portion is preferably not less than6% and not more than 50%. Thus, the effect to improve the DOF derivedfrom the diffraction light can be definitely realized while preventingan unexposed portion from being formed in a resist due to a too highshielding property of the auxiliary patterns.

In each of the first through fifth photomasks, the phase shifter ispreferably formed by trenching the transparent substrate. Thus, a verygood defocus characteristic can be exhibited in the pattern formation.

In each of the first through fifth photomasks, the semi-shieldingportion is preferably made from a metal thin film formed on thetransparent substrate. Thus, the semi-shielding portion can be easilyformed, and hence, the photomask processing can be eased.

The first pattern formation method of the invention uses any of thephotomasks of the invention, and includes the steps of forming a resistfilm on a substrate; irradiating the resist film with the exposing lightthrough the photomask of the invention; and forming a resist pattern bydeveloping the resist film having been irradiated with the exposinglight.

In the first pattern formation method, the same effects as thoseattained by each of the photomasks of the invention can obtained. Also,in the first pattern formation method, an oblique incident illuminationmethod is preferably employed in the step of irradiating the resistfilm. Thus, the contrast between regions corresponding to the mainpattern and the transparent portion can be improved in a light intensitydistribution of light having passed through the photomask. Also, thefocus characteristic of the light intensity distribution can beimproved. Accordingly, an exposure margin and a focus margin can beincreased in the pattern formation. In other words, a fine pattern canbe formed with a good defocus characteristic.

The second pattern formation method of the invention uses the second orthird photomask of the invention, and includes the steps of forming aresist film on a substrate; irradiating, through the photomask, theresist film with the exposing light emitted by annular illumination; andforming a resist pattern by developing the resist film having beenirradiated with the exposing light.

In the second pattern formation method, particularly when an average ofan outer diameter and an inner diameter of a lighting shape used in theannular illumination is not less than 0.58 and not more than 0.8,whereas values of the outer diameter and the inner diameter arestandardized by numerical aperture of an aligner, the effect to improvethe DOF of the second or third photomask of the invention can bedefinitely attained.

The third pattern formation method of the invention uses the second orthird photomask of the invention, and includes the steps of forming aresist film on a substrate; irradiating, through the photomask, theresist film with the exposing light emitted by quadrupole illumination;and forming a resist pattern by developing the resist film having beenirradiated with the exposing light.

In the third pattern formation method, particularly when a distance froma light source center to a center of each of four polarized lightingshapes used in the quadrupole illumination is not less than0.4/(0.5)^(0.5) and not more than 0.6/(0.5)^(0.5), whereas values of theouter diameter and the inner diameter are standardized by usingnumerical aperture of an aligner, the effect to improve the DOFcharacteristic of the second or third photomask can be definitelyattained.

The first mask data creation method of the invention is employed forcreating mask data for a photomask including a mask pattern formed on atransparent substrate and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the methodincludes the steps of generating a main pattern corresponding to adesired unexposed region of a resist formed by irradiating the resistwith exposing light through the photomask; determining a shape of aphase shifter that is disposed within the main pattern and transmits theexposing light in an opposite phase with respect to the transparentportion; disposing an auxiliary pattern for diffracting the exposinglight in a position on the transparent substrate away from the phaseshifter by a given distance; setting an edge of the main patterncorresponding to a boundary between the main pattern and the transparentportion as a CD adjustment edge; predicting, through simulation, adimension of a resist pattern formed by using the main pattern includingthe phase shifter and the auxiliary pattern; and changing a shape of themain pattern by moving the CD adjustment edge when the predicteddimension of the resist pattern does not accord with a desireddimension.

In the first mask data creation method, the shape of the phase shifterprovided within the main pattern and the position of the auxiliarypattern are first determined so as to optimize pattern formationcharacteristics, and thereafter, the shape of the main pattern ischanged by using the edge of the main pattern as the CD adjustment edgeso as to make the dimension of the resist pattern predicted throughsimulation accord with the desired dimension. Therefore, a mask patternwith good pattern formation characteristics can be realized.

In the first mask data creation method, the main pattern may include asemi-shielding portion that transmits the exposing light in an identicalphase with respect to the transparent portion.

In the case where the main pattern includes the semi-shielding portion,when the phase shifter is disposed at a center of a part having a givenor smaller dimension of the main pattern to be surrounded by thesemi-shielding portion, a mask pattern capable of forming a finerdesired pattern and having good pattern formation characteristics can berealized. In this case the phase shifter is preferably disposed with apart of the semi-shielding portion having a given or larger widthsandwiched between the transparent portion and the phase shifter.

In the case where the main pattern includes the semi-shielding portion,when the phase shifter is disposed in a peripheral portion of the mainpattern, a mask pattern capable of forming a desired pattern in anarbitrary shape and having good pattern formation characteristics can berealized.

In the first mask data creation method, it is preferred that the mainpattern includes a shielding portion, and that the phase shifter isdisposed at a center of a part having a given or smaller dimension ofthe main pattern to be surrounded by the shielding portion. Thus, a maskpattern capable of forming a finer desired pattern and having goodpattern formation characteristics can be realized. In this case, thephase shifter is preferably disposed with a part of the shieldingportion having a given or larger width sandwiched between thetransparent portion and the phase shifter.

The second mask data creation method of the invention is employed forcreating mask data for a photomask including a mask pattern formed on atransparent substrate and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the methodincludes the steps of generating a main pattern corresponding to adesired unexposed region of a resist formed by irradiating the resistwith exposing light through the photomask; separating the main patterninto a first region and a second region; disposing a first auxiliarypattern for diffracting the exposing light in a position on thetransparent substrate away from the first region of the main pattern bya given distance; and disposing a second auxiliary pattern fordiffracting the exposing light in a position on the transparentsubstrate away from the second region of the main pattern by anothergiven distance.

In the second mask data creation method, even in the case where thefirst region of the main pattern and the second region of the mainpattern are too close to each other to simultaneously optimally provideauxiliary patterns (diffraction light generation patterns) with respectto these regions, a diffraction light generation pattern can be disposedpriorly with respect to one of the regions of the main pattern, namely,a significant region of the main pattern. In this case, the significantregion (one of the first region and the second region) may be atransistor region.

As described so far, the present invention relates to a photomask foruse in fabrication of semiconductor integrated circuit devices.According to the invention, since an auxiliary pattern for diffractingexposing light is provided on the photomask separately from a mainpattern, the defocus characteristic of a transferred image of the mainpattern can be improved owing to diffraction light generated by theauxiliary pattern, resulting in improving the DOF characteristic.Accordingly, the present invention is particularly useful in applicationto fine pattern formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a photomask according to Embodiment 1 of theinvention and FIGS. 1B and 1C are cross-sectional views thereof takenalong line I-I of FIG. 1A;

FIGS. 2A, 2B, 2C and 2D are diagrams for showing variations of thecross-sectional structure of the photomask of Embodiment 1 of theinvention;

FIGS. 3A, 3B, 3C and 3D are diagrams for explaining that the influenceof a dimensional error in a mask on pattern formation can be reduced byemploying a mask enhancer structure for a main pattern accompanyingauxiliary patterns;

FIG. 4 is a plan view of a mask pattern of a photomask according toModification 1 of Embodiment 1 of the invention;

FIG. 5A is a diagram for explaining a diffraction phenomenon caused inexposure of a mask on which patterns are periodically arranged, FIG. 5Bis a diagram for explaining a diffraction phenomenon caused in obliqueincident exposure performed under conditions that 0th-order diffractionlight and first-order diffraction light alone pass through a lens andr0=−r1, and FIG. 5C is a diagram for explaining a diffraction phenomenoncaused in oblique incident exposure performed under conditions that0th-order diffraction light, +first-order diffraction light and−first-order diffraction light pass through a lens;

FIG. 6A is a diagram of a point light source used in simulation for aDOF characteristic obtained in oblique incident exposure performed onthe mask of FIG. 5A while changing a pitch of pitch patterns, FIG. 6B isa diagram of the pitch patterns used in the simulation, FIG. 6C is agraph for showing the result of the simulation and FIG. 6D is a diagramfor explaining a diffraction phenomenon caused in oblique incidentexposure performed on the mask of FIG. 5A under conditions that0th-order diffraction light, first-order diffraction light andsecond-order diffraction light pass through a lens;

FIG. 7A is a diagram of pitch patterns (that is, mask enhancers arrangedsubstantially infinitely periodically) used in simulation for a DOFcharacteristic obtained by performing oblique incident exposure whilechanging the pitch of the pitch patterns on a mask and FIG. 7B is agraph for showing the result of the simulation;

FIG. 8A is a diagram of pitch patterns (that is, three mask enhancersarranged in parallel) used in simulation for a DOF characteristicobtained by performing oblique incident exposure while changing thepitch of the pitch patterns on a mask and FIG. 8B is a graph for showingthe result of the simulation;

FIGS. 9A, 9B and 9C are plan views of mask patterns according to theinvention in each of which diffraction light generation patterns(auxiliary patterns) are disposed for largely improving the DOFcharacteristic of a main pattern made from a mask enhancer;

FIG. 10A is a diagram of a pattern (mask pattern) used in simulationperformed for proving that a good DOF characteristic can be obtained bydisposing the diffraction light generation patterns in positions shownin FIGS. 9A through 9C and FIG. 10B is a diagram for showing the resultof the simulation;

FIG. 11A is a diagram for showing the result of simulation performedunder optical conditions of lens numerical aperture NA of 0.6 and sin φof 0.7×NA for proving that a good DOF characteristic can be obtained bydisposing the diffraction light generation patterns in the positionsshown in FIGS. 9A through 9C, FIG. 11B is a diagram for showing theresult of the simulation performed under optical conditions of the lensnumerical aperture NA of 0.6 and sin φ of 0.6×NA and FIG. 11C is adiagram for showing the result of the simulation performed under opticalconditions of the lens numerical aperture NA of 0.7 and sin φ of 0.7×NA;

FIGS. 12A, 12B and 12C are diagrams of patterns (mask patterns) used insimulation performed for evaluating an effect to improve a DOFcharacteristic derived from diffraction light generation patterns ofthis invention obtained with a light source having an area used, FIG.12D is a diagram of the light source used in the simulation, FIG. 12E isa graph for showing the result of the simulation for a light intensitydistribution caused in correspondence to a mask enhancer throughexposure performed on each of the mask patterns of FIGS. 12A through 12Cunder predetermined conditions, and FIG. 12F is a graph for showing theresult of simulation for a defocus characteristic of a CD of a patternwith a width of 0.1 μm formed correspondingly to a mask enhancer throughthe exposure performed on each of the mask patterns of FIGS. 12A through12C under predetermined conditions;

FIG. 13A is a diagram of a first-order diffraction light generationpattern disposed away from the center of a phase shifter by a distanceP1 in the mask pattern of FIG. 12B, FIG. 13B is a diagram for showingchange of the DOF obtained through exposure performed while changing thedistance P1 in the mask pattern of FIG. 13A, FIG. 13C is a diagram of asecond-order diffraction light generation pattern disposed away from thecenter of the first-order diffraction light generation pattern by adistance P2 in the mask pattern of FIG. 12C and FIG. 13D is a diagramfor showing change of the DOF obtained through exposure performed whilechanging the distance P2 in the mask pattern of FIG. 13C;

FIGS. 14A, 14B, 14C and 14D are diagrams for explaining the result ofsimulation in which oblique incident exposure is performed on the maskpatterns of FIGS. 9A through 9C by using annular illumination;

FIGS. 15A, 15B, 15C and 15D are diagrams for explaining the result ofsimulation in which oblique incident exposure is performed on the maskpatterns of FIGS. 9A through 9C by using dipole illumination;

FIGS. 16A, 16B, 16C and 16D are diagrams for explaining the result ofsimulation in which oblique incident exposure is performed on the maskpatterns of FIGS. 9A through 9C by using quadrupole illumination;

FIGS. 17A, 17B, 17C and 17D are diagrams for explaining that a goodpattern formation characteristic can be realized by using a maskenhancer structure for attaining a preferable effect in accordance witharrangement of auxiliary patterns according to Modification 3 ofEmbodiment 1 of the invention;

FIGS. 18A, 18B, 18C and 18D are diagrams for explaining the result ofsimulation for dependency of a DOF and an exposure margin on the widthof an auxiliary pattern obtained through exposure performed on the maskpattern of FIG. 4;

FIG. 19 is a plan view of a photomask according to Embodiment 2 of theinvention;

FIG. 20A is a plan view of a photomask according to Embodiment 3 of theinvention and FIG. 20B is a cross-sectional view thereof taken alongline XX-XX of FIG. 20A;

FIGS. 21A, 21B and 21C are diagrams for showing variations of thecross-sectional structure taken along line XX-XX of FIG. 20A;

FIG. 22 is a plan view of a photomask according to a modification ofEmbodiment 3 of the invention;

FIG. 23A is a plan view of a photomask according to Embodiment 4 of theinvention and FIGS. 23B and 23C are cross-sectional views thereof takenalong line XXIII-XXIII of FIG. 23A;

FIG. 24 is a plan view of a photomask according to a modification ofEmbodiment 4 of the invention;

FIG. 25A is a plan view of an example of a simplified photomaskaccording to the modification of Embodiment 4 and FIGS. 25B and 25C arecross-sectional views thereof taken along line XXV-XXV of FIG. 25A;

FIG. 26 is a plan view of another example of the simplified photomaskaccording to the modification of Embodiment 4 of the invention;

FIG. 27 is a plan view of another example of the simplified photomaskaccording to the modification of Embodiment 4 of the invention;

FIGS. 28A, 28B, 28C and 28D are cross-sectional views for showingprocedures in a pattern formation method according to Embodiment 5 ofthe invention;

FIGS. 29A, 29B, 29C, 29D and 29E are diagrams for showing principalmethods for calculating an oblique incident angle defined by the presentinventor for calculating appropriate positions of diffraction lightgeneration patterns also in using a light source having an area;

FIG. 30 is a flowchart of a mask data creation method according toEmbodiment 6 of the invention;

FIGS. 31A, 31B, 31C, 31D, 31E, 31F and 31G are diagrams of specificexamples of mask patterns formed in the respective procedures of themask data creation method of Embodiment 6;

FIG. 32 is a diagram of a detailed example of a diffraction lightgeneration pattern formed by the mask data creation method of Embodiment6;

FIG. 33 is a flowchart of improved processing of the mask data creationmethod of Embodiment 6;

FIG. 34 is a diagram of a detailed example of a diffraction lightgeneration pattern formed through the improved processing of the maskdata creation method of Embodiment 6;

FIG. 35 is a plan view of a conventional photomask; and

FIG. 36 is a plan view of another conventional photomask.

DETAILED DESCRIPTION OF THE INVENTION

(Prerequisites)

Prerequisites for explaining preferred embodiments of the invention willbe first described.

Since a photomask is generally used in a reduction projection typealigner, it is necessary to consider a reduction ratio in arguing apattern dimension on the mask. However, in order to avoid confusion, inthe description of each embodiment below, when a pattern dimension on amask is mentioned in correspondence to a desired pattern to be formed(such as a resist pattern), a value obtained by converting the patterndimension by using a reduction ratio (magnification) is used unlessotherwise mentioned. Specifically, also in the case where a resistpattern with a width of 100 nm is formed by using a mask pattern with awidth of M×100 nm in a 1/M reduction projection system, the width of themask pattern and the width of the resist pattern are both described as100 nm.

Also, in each embodiment of the invention, M and NA respectivelyindicate a reduction ratio and numerical aperture of a reductionprojection optical system of an aligner, λ indicates the wavelength ofexposing light and φ indicates an oblique incident angle in obliqueincident exposure unless otherwise mentioned.

Embodiment 1

A photomask according to Embodiment 1 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 1A is a plan view of the photomask of Embodiment 1, FIG. 1B is anexemplified cross-sectional view thereof taken along line I-I of FIG.1Aand FIG. 1C is another exemplified cross-sectional view thereof takenalong line I-I of FIG. 1A.

As shown in FIG. 1A and 1B, a line-shaped main pattern 101 to betransferred through exposure is provided on a transparent substrate 100.The main pattern 101 is composed of a first semi-shielding portion 101Ahaving first transmittance for partially transmitting exposing light anda phase shifter 101B. The first semi-shielding portion 101A is formed soas to surround the line-shaped phase shifter 101B. In other words, thephase shifter 101B is formed at the center of the main pattern 101. Thephase shifter 101B is formed by, for example, trenching the transparentsubstrate 100. On both sides of the main pattern 101 on the transparentsubstrate 100, a pair of auxiliary patterns 102 that diffract theexposing light and are not transferred through the exposure are providedwith transparent portions sandwiched between the main pattern 101 andthe auxiliary patterns 102. The auxiliary patterns 102 are made from asecond semi-shielding portion having second transmittance for partiallytransmitting the exposing light. In this case, the first semi-shieldingportion 101A and the second semi-shielding portion are, for example, asemi-shielding film 106 formed on the transparent substrate 100. It isnoted that the first semi-shielding portion 101A and the auxiliarypatterns 102 may be shielding portions.

In the photomask shown in FIGS. 1A and 1B, a mask pattern consists ofthe main pattern 101 and the auxiliary patterns 102. Also, an area onthe transparent substrate 100 on which the mask pattern is not formedcorresponds to the transparent portion (opening).

Furthermore, there is a relationship of opposite phases between lightpassing through the phase shifter 101B and light passing through thetransparent portion (specifically, a relationship that a phasedifference between these lights is not less than (150+360×n) degrees andnot more than (210+360×n) degrees (wherein n is an integer)).

Moreover, there is a relationship of the identical phase between lightspassing through the first semi-shielding portion 101A and the secondsemi-shielding portion (the auxiliary patterns 102) and light passingthrough the transparent portion (specifically, a relationship that aphase difference between these lights is not less than (−30+360×n)degrees and not more than (30+360×n) degrees (wherein n is an integer).

According to Embodiment 1, since the main pattern 101 is composed of thefirst semi-shielding portion (or the first shielding portion) 101A andthe phase shifter 101B, the lights passing through the transparentportion and the first semi-shielding portion 101A (the lights in theidentical phase) can be partially cancelled by the light passing throughthe phase shifter 101B (the light in the opposite phase), so that astrong shielding property can be realized. This effect is particularlyremarkable when the main pattern 101 is a fine pattern and hence itsshielding property is weak. On the other hand, since the auxiliarypattern 102 is made from the semi-shielding portion, its shieldingproperty is weak. Therefore, while increasing the shielding degree of ashielded image corresponding to the main pattern 101 as compared withthat attained by a general shielding pattern, the shielding property ofthe auxiliary patterns 102 can be reduced. Accordingly, the contrast ina light intensity distribution can be emphasized by employing the maskstructure of this embodiment. Also, since the auxiliary patterns 102having low transmittance are provided separately from the main pattern101, diffraction light that interferes with the light passing throughthe phase shifter 101B of the main pattern 101 can be generated bydisposing the auxiliary patterns 102 in appropriate positions.Accordingly, a defocus characteristic of a transferred image of the mainpattern 101 can be improved, resulting in improving the DOFcharacteristic.

The following description is given under assumption that the mainpattern is composed of the phase shifter and the semi-shielding portion,and unless otherwise mentioned, similar effects can be attained evenwhen the main pattern is composed of a phase shifter and a shieldingportion.

According to Embodiment 1, since the auxiliary patterns 102 are thesemi-shielding portions with a weak shielding property, the auxiliarypatterns 102 are minimally transferred through the exposure. Thisincreases the degree of freedom in the arrangement of the auxiliarypatterns under restriction that the auxiliary patterns 102 are nottransferred. Accordingly, the periodicity in the whole patternarrangement including the main pattern 101 can be increased, so that theDOF characteristic can be further improved. Also, since the auxiliarypatterns 102 are the semi-shielding portion, the auxiliary patterns 102can be made thick under restriction that they are not transferredthrough the exposure. Therefore, the photomask can be processed easily,and even if a dimensional error is caused in formation of the auxiliarypatterns, the dimensional error less affects the transferred image ofthe main pattern 101. Furthermore, according to this embodiment, in thecase where the peripheral portion of the main pattern 101 is made fromthe semi-shielding portion, a dimensional error of the main pattern 101caused in the mask processing less affects the pattern formation.

Also, according to Embodiment 1, since the phase shifter 101B isprovided at the center of the main pattern 101, the contrast in thelight intensity distribution at the center of the shielded imagecorresponding to the main pattern 101 can be emphasized, so that, forexample, a fine line pattern can be formed while keeping a good defocuscharacteristic.

Furthermore, according to Embodiment 1, the phase shifter 101B is formedby forming an opening in the semi-shielding portion (i.e., thesemi-shielding film 106) and trenching the transparent substrate 100within the opening. Therefore, the phase shifter can attain hightransmittance. Also, the intensity of the light in the opposite phasepassing through the inside of the main pattern (i.e., the phase shifter101B) can be controlled in accordance with the size of the openingformed in the semi-shielding portion. Therefore, the light in theopposite phase passing through the main pattern 101 can be easilyoptimized, so that a very good defocus characteristic can be exhibitedin the pattern formation. In other words, the mask dimension can becontrolled in accordance with the width of a part of the semi-shieldingportion surrounding the phase shifter, and in addition, the intensity ofthe light in the opposite phase can be controlled in accordance with thedimension of the opening formed in the semi-shielding portion.Therefore, as a peculiar effect of this embodiment, the mask dimensionand the intensity of the light in the opposite phase can beindependently controlled. As a result, while definitely realizing theeffects attained by controlling the light in the opposite phase, such asthe effect to improve the focus characteristic and the effect to improvethe contrast of a fine pattern, a desired pattern dimension can beeasily realized.

In Embodiment 1, the first transmittance of the first semi-shieldingportion 101A included in the main pattern 101 is preferably 15% or less.Thus, in the pattern formation using the photomask, a resist film can beprevented from reducing in its thickness due to too much light passingthrough the semi-shielding portion or resist sensitivity can beoptimized. In other words, such an effect as well as the effect toimprove the DOF characteristic and the effect to improve the contrastcan be both realized.

Also, in Embodiment 1, the second transmittance of the auxiliarypatterns 102 (i.e., the second semi-shielding portion) is preferably notless than 6% and not more than 50%. Thus, while preventing an unexposedportion from being formed in a resist due to a too high shieldingproperty of the auxiliary patterns 102, the effect to improve the DOFcharacteristic derived from the diffraction light can be definitelyrealized.

Furthermore, in Embodiment 1, the first semi-shielding portion 101A andthe second semi-shielding portion working as the auxiliary patterns 102may be made from the same semi-shielding film 106 such as a metal thinfilm formed on the transparent substrate 100. In this case, therespective semi-shielding portions can be easily formed, and hence, thephotomask can be easily processed. As the metal thin film, a thin film(with a thickness of approximately 50 nm or less) of a metal such as Cr(chromium), Ta (tantalum), Zr (zirconium), Mo (molybdenum) or Ti(titanium), or an alloy of any of these metals can be used. Examples ofthe alloy are Ta—Cr alloy, Zr—Si alloy, Mo—Si alloy and Ti—Si alloy.Alternatively, a thick film including a silicon oxide such as ZrSiO,CrAlO, TaSiO, MoSiO or TiSiO may be used instead of the metal thin film.

Furthermore, also in the case where merely the first semi-shieldingportion 101A of the main pattern 101 of Embodiment 1 is replaced with ashielding portion, the effect to improve the contrast attained by usingthe main pattern 101 and the auxiliary patterns 102 can be exhibited.Specifically, for example, as shown in FIG. 1C, a mask structure inwhich a shielding film 107 is further deposited on the semi-shieldingfilm 106 used for forming the first semi-shielding portion 101A may beemployed.

FIGS. 2A through 2D show variations of the photomask structure accordingto Embodiment 1. In other words, the mask structure shown in FIG. 1B canbe replaced with a structure shown in FIG. 2A. In FIG. 2A, a phase shiftfilm 108 made from a material with high transmittance and asemi-shielding film 106 are successively formed on a transparentsubstrate 100, the phase shift film 108 is removed in a formation regionfor the phase shifter 101B provided within the main pattern 101 and thesemi-shielding film 106 is removed in formation regions for the phaseshifter 101B and the transparent portion. Also in this case, a shieldingfilm 107 may be deposited on the semi-shielding film 106 used forforming the first semi-shielding portion 101A of the main pattern 101 asshown in FIG. 2B. It is noted that in the mask structure shown in FIG.2A or 2B, an area on the transparent substrate 100 in which the phaseshift film 108 alone is formed corresponds to the transparent portion.When such a structure is employed, the phase of the phase shifter 101Bcan be controlled in accordance with the thickness of the phase shiftfilm 108, and hence, the phase of the phase shifter 101B can beaccurately controlled.

Alternatively, the mask structure of FIG. 1B can be replaced with astructure shown in FIG. 2C. In FIG. 2C, a semi-shielding film 106 and aphase shift film 108 made from a material with high transmittance aresuccessively formed on a transparent substrate 100, the semi-shieldingfilm 106 is removed in a transparent portion formation region and thephase shift film 108 is removed in a region other than a phase shifterformation region within the main pattern 101. In this case, a multilayerstructure composed of the phase shift film 108 and a shielding film 107may be formed on the semi-shielding film 106 used for forming the firstsemi-shielding portion 101A of the main pattern 101 as shown in FIG. 2D.When such a structure is employed, the phase of the phase shifter 101Bcan be controlled in accordance with the thickness of the phase shiftfilm 108.

Next, a method for improving the resolution of a line pattern byemphasizing the shielding property of a mask pattern by employing thestructure in which a phase shifter (namely, the phase shifter 101B) isprovided at the center of a line-shaped shielding pattern (namely, themain pattern 101) (hereinafter which structure is referred to as themask enhancer structure and which method is referred to as the centerline enhancement method), which has been found by the present inventor,will be described. The following description is given by exemplifyingthe case where a fine line pattern is formed by the positive resistprocess. Also in the case where the negative resist process is used, thecenter line enhancement method can be similarly practiced by replacing afine line pattern (a resist pattern) of the positive resist process witha fine space pattern (a resist removal pattern). Also, it is assumed forsimplification in the following description that a shielding patternexcluding a phase shifter is made from a shielding portion.

In a mask enhancer, when the pattern width and the width of the phaseshifter are adjusted so that the intensity of light rounding from theperiphery of the shielding pattern to the reverse face thereof canbalance with the intensity of light passing through the phase shifter,the amplitude intensity of light passing through the mask enhancer has adistribution where the amplitude intensity is 0 (zero) in a positioncorresponding to the center of the mask enhancer. In this case, also theintensity of the light passing through the mask enhancer (which is asquare of the amplitude intensity) has a distribution where theintensity is 0 (zero) in the position corresponding to the center of themask enhancer. In other words, an image with high contrast can be formedby using the mask enhancer. In this case, even when the shieldingportion is a semi-shielding portion that transmits light in theidentical phase with respect to the transparent portion (transparentsubstrate) and has finite transmittance, the same effect can beattained. Specifically, in consideration of the weak shielding property,a semi-shielding portion is not preferred as a line-shaped mask pattern,but when a phase shifter is provided within the semi-shielding portion,namely, when the mask enhancer structure is employed, an image with highcontrast can be formed. In other words, a semi-shielding portion can beutilized for fine pattern formation.

As described above, the center line enhancement method is veryeffective, due to its principle, in a state where a pattern composed ofa completely shielding portion alone (a completely shielding pattern) isdifficult to form on a mask. Specifically, the center line enhancementmethod can exhibit its effect when the width of a mask pattern is toosmall to shield light by using the completely shielding pattern due todiffraction, namely, when the mask pattern has a width of 0.8×λ/NA orless, and the center line enhancement method can exhibit its effect moreremarkably when the mask pattern has a width of 0.5×λ/NA or less, wherethe influence of the diffraction is large. Furthermore, the center lineenhancement method can exhibit its effect very remarkably when the maskpattern has a width of 0.4×λ/NA or less, where pattern formation using acompletely shielding pattern is very difficult. Accordingly, in thisembodiment employing the mask enhancer structure for the main pattern,the effect is exhibited particularly when the mask width of the mainpattern has a very small dimension as described above, and hence, thisembodiment is highly effective in formation of a fine pattern. It isnoted that the width of the mask pattern of the mask enhancer structureherein means a width of the whole outline shape of the shielding portionor the semi-shielding portion including the phase shifter.

Now, it will be described that the influence of a dimensional error of amask on the pattern formation can be reduced by employing the maskenhancer structure for a main pattern accompanying an auxiliary pattern.

When an auxiliary pattern is added in the vicinity of a main pattern,the resultant mask pattern is densely arranged. In general, in a denselyarranged mask pattern, the influence of a dimensional error of the maskon the pattern formation is large. When the mask enhancer structure isused for the main pattern, however, this influence can be reduced.

FIG. 3A is a diagram of a mask pattern consisting of a main pattern 101with the mask enhancer structure including a phase shifter 101B and asemi-shielding portion 101A and auxiliary patterns 102 made from asemi-shielding portion. Specifically, the mask pattern is composed ofthe main pattern 101 with a width of 140 nm and the auxiliary patterns102 with a width of 90 nm each having its center away from the center ofthe main pattern 101 by 300 nm. In the mask enhancer structure of themain pattern 101, the phase shifter 101B has a width of 70 nm. In thecase where auxiliary patterns 102 are the same as those of the maskpattern of FIG. 3A and the main pattern 101 is simply made from ashielding portion (shielding pattern) 109 as in FIG. 3B, it is necessaryto provide a width of 180 nm to the shielding pattern in order to attaina shielding property equivalent to that attained by the mask enhancerstructure of FIG. 3A.

FIGS. 3C and 3D are diagrams for respectively showing the results ofsimulation for the influence on the pattern formation when the mainpattern widths and the auxiliary pattern widths of the mask patterns ofFIGS. 3A and 3B are simultaneously changed by 10 nm, respectively.Specifically, FIG. 3C shows the result of simulation for a lightintensity distribution caused in a position corresponding to lineIIIA-IIIA (along a widthwise direction of the main pattern 101) of FIG.3A through pattern exposure, and FIG. 3D shows the result of simulationfor a light intensity distribution caused in a position corresponding toline IIIB-IIIB (along a widthwise direction of the main pattern 101) ofFIG. 3B through pattern exposure. In the simulation, the wavelength λ ofa light source is 193 nm (which is the wavelength of an ArF lightsource) and the lens numerical aperture NA is 0.6. Also, all thesemi-shielding portions used in the mask patterns have transmittance of6%. In FIGS. 3C and 3D, a result obtained by increasing each patternwidth (mask dimension) by 10 nm (+10 nm) is shown with a solid line anda result obtained by reducing each pattern width by 10 nm (−10 nm) isshown with a broken line. Also, in FIGS. 3C and 3D, a positioncorresponding to the center of the main pattern 101 is set to 0 (zero).

It is understood from the simulation results shown in FIGS. 3C and 3Dthat the light intensity at the center of the main pattern is minimallychanged against the change of the mask dimension when the main patternhas the mask enhancer structure. Also, in the evaluation by using thedimension of a pattern to be formed, when the main pattern width and theauxiliary pattern width, namely, the mask dimension, are increased by 10nm under conditions that a pattern with a width of 100 nm is formed byusing the mask structure of FIG. 3A, the width of the pattern to beformed is 106 nm. Similarly, when the mask dimension is reduced by 10nm, the width of the pattern to be formed is 95 nm. Specifically, evenwhen the mask dimension is increased/reduced by approximately 10 nm, thedimension of the pattern to be formed is affected by merelyapproximately 5 nm.

On the other hand, when the mask dimension of the main pattern and theauxiliary pattern is increased by 10 nm under conditions that a patternwith a width of 100 nm is formed by using the mask structure of FIG. 3B,the dimension of the pattern to be formed is 116 nm. Similarly, when themask dimension is reduced by 10 nm, the dimension of the pattern to beformed is 86 nm. Specifically, when the mask dimension isincreased/reduced by 10 nm, the dimension of the pattern to be formed isincreased/reduced by as much as approximately 15 nm. In other words,when the mask structure of FIG. 3B is used, the pattern dimension ischanged more largely than the variation of the mask dimension, andhence, a mask dimension error can largely affect the pattern formation.

In this manner, when the mask enhancer structure is employed for a mainpattern disposed in the vicinity of an auxiliary pattern, an effect tosuppress the influence of mask dimension variation on the patternformation can be attained. This effect is particularly remarkable in themask enhancer structure in which a main pattern is composed of a phaseshifter and a semi-shielding portion, but a similar effect can beattained in a mask enhancer structure in which a main pattern iscomposed of a phase shifter and a shielding portion.

In this embodiment, the auxiliary patterns are not necessarily providedon the both sides of the main pattern. Specifically, in the case where amain pattern is disposed in the vicinity of one side of another mainpattern, an auxiliary pattern may be provided merely on the otheropposite side of the main pattern.

Modification 1 of Embodiment 1

A photomask according to Modification 1 of Embodiment 1 will now bedescribed with reference to the accompanying drawings.

FIG. 4 is a plan view of a mask pattern of the photomask according toModification 1 of Embodiment 1. In FIG. 4, like reference numerals areused to refer to like elements of the photomask of Embodiment 1 shown inFIGS. 1A and 1B, so as to omit the description.

As a first characteristic of this modification, each auxiliary pattern102 (with a width D1) is disposed in a position away from the center ofa phase shifter 101B (with a width W) of a main pattern 101 (with awidth L) by a distance λ/(2×sin φ) with respect to a predeterminedoblique incident angle φ.

As a second characteristic of this modification, a second auxiliarypattern 103 (with a width D2) that diffracts the exposing light and isnot transferred through the exposure is disposed in a position away fromthe center of the phase shifter 101B of the main pattern 101 by adistance λ/(2×sin φ)+λ/(NA+sin φ), namely, in a position away from thecenter of the auxiliary pattern 102 (hereinafter referred to as thefirst auxiliary pattern) by a distance λ/(NA+sin φ). There is atransparent portion sandwiched between the first auxiliary pattern 102and the second auxiliary pattern 103. Also, the second auxiliary pattern103 is made from a semi-shielding portion similarly to the firstauxiliary pattern 102.

According to this modification, the effect to improve the DOF attainedby providing the auxiliary patterns can be definitely realized.

It is noted that either of the first auxiliary patterns 102 and thesecond auxiliary patterns 103 may be omitted in this modification.

Also, in this modification, the aforementioned effect can be attained tosome extent even when the distance between the center of the phaseshifter 101B and the center of the first auxiliary pattern 102 isapproximate to λ/(2×sin φ).

Furthermore, in this modification, the aforementioned effect can beattained to some extent even when the distance between the center of thephase shifter 101B and the center of the second auxiliary pattern 103 isapproximate to λ/(2×sin φ)+λ(NA+sin φ).

Also, in this modification, the oblique incident angle (φ is preferablynot less than 0.40×NA and not more than 0.80×NA, and more preferably,not less than 0.58×NA and not more than 0.70×NA. In the case whereannular illumination is used for the exposure, the oblique incidentangle φ is preferably not less than 0.60×NA and not more than 0.80×NA.In the case where quadrupole illumination is used for the exposure, theoblique incident angle φ is preferably not less than 0.40×NA and notmore than 0.60×NA (which will be described in detail in Modification 2of Embodiment 1 below.)

Furthermore, in this modification, the width L of the main pattern 101is larger than the width W of the phase shifter 101B preferably by atleast 2×20 nm (in the actual dimension on the mask), and more preferablyby at least a twice of a quarter of the exposure wavelength (i.e., thewavelength of the exposing light). Specifically, in the mask enhancerstructure of the main pattern, a part of the semi-shielding portion (orthe shielding portion) sandwiched between the phase shifter and thetransparent portion has a width preferably of 20 nm or more (in theactual dimension on the mask) and more preferably of a quarter or moreof the exposure wavelength. Since this photomask employs the maskenhancer structure, the main pattern preferably has a width of 0.8×λ/NAor less, and accordingly, the part of the semi-shielding portion (or theshielding portion) sandwiched between the phase shifter and thetransparent portion has a width preferably not exceeding 0.4×λ/NA (whichwill be described in detail in Modification 3 of Embodiment 1 below).

In addition, in this modification, the width D2 of the second auxiliarypattern 103 is preferably larger than the width D1 of the firstauxiliary pattern 102, and more particularly, the width D2 is preferably1.2 times as large as the width D1 (which will be described in detail inModification 4 of Embodiment 1 below).

Now, the reason why the defocus characteristic can be improved in thepattern formation when diffraction light that interferes with lightpassing through the opening (the phase shifter 101B) provided within themask enhancer is generated by disposing the diffraction light generationpatterns (auxiliary patterns 102) in the above-described specifiedpositions against the main pattern 101 having the mask enhancerstructure will be described.

FIG. 5A is a diagram for explaining a diffraction phenomenon caused whenexposure is performed on a mask on which patterns are periodicallyarranged. As shown in FIG. 5A, a mask 150 in which a plurality ofshielding patterns (hereinafter referred to as the pitch patterns) 151are substantially infinitely periodically arranged at predeterminedpitch P is irradiated with light 141 emitted from a light source 140.Herein, “to be substantially infinitely periodically arranged” meansthat the pitch pattern 151 disposed at the center of the mask can attainan effect attained by each of a substantially infinite number of pitchpatterns periodically arranged. In other words, it means that the pitchpatterns 151 are disposed so that a distance from a pitch pattern 151disposed at the center of the mask to another pitch pattern 151 disposedat the edge of the mask can be approximately 4×λ/NA or more.

FIG. 5A shows the diffraction phenomenon caused in assuming the obliqueincident exposure. Specifically, the light source 140 is disposed in aposition away from the normal line (indicated with a long dashed shortdashed line in the drawing) extending through the center of a lens 152by a distance S. In this case, the incident angle (the oblique incidentangle) φ of the light 141 from the light source 140 against the mask 150is represented as sin φ=S×NA. Herein, the distance S used for definingthe oblique incident angle φ is designated as an oblique incidentposition. The coordinate of the light source 140 is represented by usinga value standardized by the numerical aperture NA. Also, the diffractionangle θn of nth-order diffraction light (wherein n is an integer) of thelight 141 having passed through the pitch patterns 151 arranged at thepitch P is represented as sin θn=n×λ/P. Also, 0th-order diffractionlight 142 of the light 141 having entered the mask 150 at the obliqueincident angle φ reaches a position expressed as a coordinate r0=−sinφ=−S×NA on the lens 152 (a coordinate on a one-dimensional coordinatesystem having the lens center as the origin; which applies tocoordinates mentioned below). Furthermore, first-order diffraction light(+first-order diffraction light) 143 of the light 141 reaches a positionexpressed as a coordinate r1=r0+sin θ1=r0+λ/P. In general, a position onthe lens 152 where nth-order diffraction light reaches is expressed as acoordinate rn=r0+sin θn=r0+n×λ/P, whereas when the absolute value of rnexceeds NA, the nth-order diffraction light is not diffraction lightpassing through the lens 152, and hence is not focused on a wafer.

In an ideal lens, phase change caused in defocus of diffraction lightthat passes through the lens and is focused on a wafer is determinedmerely by the distance (radius) from the lens center to a position ofthe lens through which the diffraction light passes. In the case wherelight enters the lens perpendicularly, 0th-order diffraction lightalways passes through the lens center and first-order or higher orderdiffraction lights pass through positions away from the lens center.Therefore, in defocus, a phase difference is caused between the0th-order diffraction light passing through the lens center and thehigher order diffraction light passing through a position away from thelens center, which results in image defocus.

FIG. 5B is a diagram for explaining a diffraction phenomenon caused whenthe mask of FIG. 5A is subjected to the oblique incident exposure underconditions that the 0th-order diffraction light and the first-orderdiffraction light alone pass through the lens and r0=−r1. As shown inFIG. 5B, the 0th-order diffraction light 142 and the first-orderdiffraction light 143 pass through positions away from the center of thelens 152 by the same distance. Therefore, the phase change caused indefocus is identical between the 0th-order diffraction light 142 and thefirst-order diffraction light 143. Specifically, no phase difference iscaused between these diffraction lights, so that image defocus derivedfrom the defocus can be avoided. At this point, in consideration ofr0=−r1, r1=r0+sin θ1 can be modified to −2×r0=sin θ1. Furthermore, inconsideration of sin θ1=λ/P and r0=−sin φ, 2×sin φ=λ/P can be obtained.Accordingly, through the oblique incident exposure with the obliqueincident angle φ expressed as sin φ=λ/(2×P), pattern formation with agood defocus characteristic can be performed. In other words, in theoblique incident exposure with the oblique incident angle φ, a gooddefocus characteristic can be attained when periodical patterns areprovided on a mask with a pitch P of λ/(2×sin φ). This is why thedefocus characteristic can be improved by using substantially infinitelyperiodically arranged pitch patterns in the oblique incident exposure.

However, it is only when the pitch P is equal to or approximate toλ/(2×sinφ) that the aforementioned good defocus characteristic can beobtained. Also, this effect to improve the defocus characteristic can beobtained under conditions that diffraction lights passing through thelens are the 0th-order diffraction light and one of the +first-orderdiffraction light and the −first-order diffraction light.

FIG. 5C is a diagram for explaining a diffraction phenomenon caused whenthe mask of FIG. 5A is subjected to the oblique incident exposure underconditions that the 0th-order diffraction light, the +first-orderdiffraction light and the −first-order diffraction light pass throughthe lens. As shown in FIG. 5C, even under conditions that the 0th-orderdiffraction light 142 passes through a position on the lens 152expressed by the coordinate r0=−sin φ and the +first-order diffractionlight 143 passes through a position on the lens 152 expressed by thecoordinate r1=sin φ, a good defocus characteristic cannot be obtained ifthe coordinate r0−sin θ of a position on the lens 152 where the−first-order diffraction light 144 passes is within the lens 152. Atthis point, a condition that the −first-order diffraction light 144passes out of the lens 152 is expressed as r0−sin θ1<−NA. Also, inconsideration of r0=−sin φ and sin θ1=r1−r0=2×sin φ, the condition thatthe −first-order diffraction light 144 passes out of the lens 152 isexpressed as −sin φ−2×sin φ<−NA, namely, 3×sin φ>NA.

In other words, a condition that both the +first-order diffraction lightand the −first-order diffraction light pass through the lens inemploying the oblique incident angle φ is expressed as 3×sin φ<NA. Whenthe oblique incident angle φ satisfies this condition, both the+first-order diffraction light and the −first-order diffraction lightpass through the lens and the distances from the lens center to thepositions where the +first-order diffraction light and the −first-orderdiffraction light respectively pass through the lens are different fromeach other. Therefore, the image defocus is caused due to a phasedifference between these diffraction lights in defocus. Accordingly, thelower limit of the oblique incident angle φ for realizing theimprovement of the defocus characteristic is defined as sin φ>NA/3.Considering that the 0th-order diffraction light does not pass throughthe lens when sin φ exceeds NA, a condition of the oblique incidentangle φ for improving the defocus characteristic is expressed as NA>sinφ>NA/3.

Next, the result of simulation for a DOF characteristic obtained in theoblique incident exposure performed on the mask of FIG. 5A with thepitch of the pitch patterns changed will be described. FIG. 6A is adiagram of a point light source used in the simulation, FIG. 6B is adiagram of pitch patterns used in the simulation, and FIG. 6C is a graphfor showing the result of the simulation for the DOF characteristic. Inthe simulation for the DOF characteristic, a pair of light sources(point light sources) 140 shown in FIG. 6A are used, and specifically,the pair of point light sources 140 are positioned in coordinates (lightsource coordinates), on a plane perpendicular to the normal lineextending through the center of the lens 152 (a two-dimensionalcoordinate system), of (−0.8, 0) and (0.8, 0). In this case, the pointlight sources 140 are ArF light sources (with a wavelength λ of 193 nm).Also, in the simulation for the DOF characteristic, the oblique incidentexposure is performed with the lens numerical aperture NA set to 0.6 andthe oblique incident angle φ set to satisfy sin φ=0.48 (namely, thedistance S of FIG. 5A set to 0.8). Furthermore, the pitch patterns 151shown in FIG. 6B, namely, the pitch patterns 151 infinitely periodicallyarranged at the pitch P, are line-shaped shielding patterns each with awidth of 100 nm, and formation of a pattern with a width of 100 nm byusing the pitch pattern 151 is simulated. A value of the DOF shown inFIG. 6C is a range of the defocus in which a pattern having a width of100 nm can be formed with a dimensional error of 10 nm or less. As shownin FIG. 6C, in the case where the pitch P of the pitch patterns 151 isequal to or approximate to λ/(2×sin φ) (i.e., approximately 0.20 μm), avery large DOF can be obtained. However, when the pitch P is smaller orlarger than λ/(2×sin φ), the value of the DOF is abruptly reduced.

At this point, the present inventor has paid attention, in thedependency of the DOF on the pitch shown in FIG. 6C, to that values ofthe pitch P for locally improving the DOF are present at equal intervalswhen the pitch P is changed. Furthermore, the present inventor has foundthat the values of the pitch P for locally improving the DOF areobtained by multiplying λ/(NA+sin φ) (i.e., approximately 1.8 μm) by anintegral number, at which high-order diffraction light affects imagefocus. This will be described as follows:

In a diffraction phenomenon of light, diffraction lights of one orderand another adjacent order have opposite phases. FIG. 6D is a diagramfor explaining a diffraction phenomenon caused when the mask of FIG. 5Ais subjected to the oblique incident exposure under conditions that the0th-order diffraction light, the first-order diffraction light and thesecond-order diffraction light pass through the lens. In this case, thesecond-order diffraction light 145 of FIG. 6D has a phase opposite tothat of the first-order diffraction light 143. When an image formed bythe 0th-order diffraction light 142 and the first-order diffractionlight 143 through the oblique incident exposure is interfered by animage formed by the second-order diffraction light 145 in the oppositephase, these images mutually cancel the intensity of the oppositeimages. In the defocus, however, although the intensities of theseimages are reduced, since the first-order diffraction light 143 and thesecond-order diffraction light 145 are in the opposite phases,degradation in the respective images caused by the defocus can bemutually cancelled. In other words, in an image resulting from theinterference between the image formed by the first-order diffractionlight 143 and the image formed by the second-order diffraction light 145in the opposite phase, the defocus characteristic is improved, resultingin improving the DOF characteristic.

A condition for thus improving the DOF characteristic corresponds to acondition that the second-order diffraction light 145 passes through thelens 152 as shown in FIG. 6D, which is expressed as sin θ2<NA−r0. Atthis point, in consideration of sin θ2=2×λ/P and r0=−sin φ, theaforementioned condition is expressed as 2×λ/P<NA+sin φ. Accordingly,pitch P for changing a state where lights up to the first-orderdiffraction light 143 pass through the lens 152 to a state where lightsup to the second-order diffraction light 145 pass through the lens 152is expressed as 2×λ/(sin φ+NA). Also, in general, a condition thatnth-order diffraction light passes through a lens is expressed as sinθn=n×λ/P<NA−r0=NA+sin φ. In other words, the nth-order diffraction lightcan pass through the edge of a lens when the pitch P is n×λ/(sin φ+NA)or more. Accordingly, the DOF characteristic is locally improved whenthe pitch P is n×λ/)(sin φ+NA) (wherein n is an integer of 2 or more).

As described above, the defocus characteristic can be improved in theoblique incident exposure by utilizing interference between lights inthe opposite phases. Therefore, the present inventor has concluded thatthe defocus characteristic can be improved through an operation forcausing a function equivalent to that caused by increasing the intensityof the second-order diffraction light in the opposite phase to thefirst-order diffraction light. Specifically, the defocus characteristiccan be improved through an operation for introducing, into diffractionlights generated by periodically arranging shielding patterns, acomponent of the 0th-order diffraction light in the opposite phase tothe first-order diffraction light. This operation can be realized byutilizing the above-described mask enhancer structure. Specifically, inthe mask enhancer, light in the opposite phase can be controlled bycontrolling the dimension of the phase shifter (the opening) providedwithin the mask enhancer while adjusting the degree of shieldingattained by the mask enhancer without changing the order of diffractionlight passing through the lens. The present inventor has presumed thatwhen the mask enhancer is employed, the DOF locally slightly improvedwhen the pitch P is n×λ/(sin φ+NA) (wherein n is an integer of 2 ormore) (see FIG. 6C) can be largely improved in proportion to thedimension of the phase shifter of the mask enhancer.

Therefore, the result of simulation performed similarly to thesimulation shown in FIG. 6A through 6C by the present inventor by usinga mask enhancer as the pitch patterns will now be described. FIG. 7A isa diagram of mask enhancers used as the pitch patterns in thesimulation, and FIG. 7B is a graph for showing the result of thesimulation for the DOF characteristic obtained by using the pitchpatterns of FIG. 7A. Point light sources used in this simulation are thesame as those shown in FIG. 6A and the simulation is performed under thesame conditions as those employed in FIG. 6A through 6C. Furthermore,FIG. 7B also shows the result obtained by changing the size of the phaseshifter (the width of the opening) in the mask enhancer.

As shown in FIG. 7A, a plurality of mask enhancers 110 are substantiallyinfinitely periodically arranged at predetermined pitch P. Each maskenhancer 110 is composed of a semi-shielding portion 111 in the shapecorresponding to the outline of the mask enhancer and a phase shifter112 provided at the center of the mask enhancer 110 and surrounded bythe semi-shielding portion 111. In this case, the mask enhancer 110 hasa width (pattern width) L and the phase shifter 112 has a width (openingwidth) W.

Similarly to the DOF characteristic shown in FIG. 6C, in the DOFcharacteristic shown in FIG. 7B, the DOF is locally increased when thepitch P is n×λ/(sin φ+NA) (wherein n is an integer of 2 or more). Also,as the ratio of the opening width W to the pattern width L (namely, W/L)is larger, the DOF is much more largely improved. In other words, as aneffect peculiar to the mask enhancer, when patterns consisting ofperiodically arranged mask enhancers are subjected to the obliqueincident exposure, pattern transfer with a good DOF characteristic canbe performed not only when the pitch P is equal to or approximate toλ/(2×sin φ) (which is approximately 0.20 μm under the conditions for thesimulation) but also when the pitch P is as large as n×λ/)(sin φ+NA)(which is approximately n×0.18 μm under the conditions for thesimulation; wherein n is an integer of 2 or more).

Furthermore, the result of simulation performed by the present inventorsimilarly to that shown in FIGS. 6A through 6C by using, as maskenhancers working as pitch patterns, three mask enhancers arranged inparallel instead of the substantially infinitely periodically arrangedmask enhancers shown in FIG. 7A will be explained. FIG. 8A is a diagramof the mask enhancers used in the simulation and FIG. 8B is a diagramfor showing the result of the simulation for the DOF characteristicobtained by using the mask enhancers of FIG. 8A. Point light sourcesused in the simulation are the same as those shown in FIG. 6A and theother conditions for the simulation are the same as those employed inFIGS. 6A through 6C. Specifically, the oblique incident exposure isperformed with the lens numerical aperture NA of 0.6, the distance S(see FIG. 5A) set to 0.8 and the oblique incident angle φ set to satisfysin φ=S×NA=0.48.

As shown in FIG. 8A, the three mask enhancers 110 are arranged inparallel at an equal interval (i.e., a pattern distance R). Each maskenhancer 110 is composed of a semi-shielding portion 111 in the shapecorresponding to the outline of the mask enhancer and a phase shifter112 disposed at the center of the mask enhancer 110 and surrounded bythe semi-shielding portion 111. In this case, when the mask enhancer 110has a width (pattern width) L and the phase shifter 112 has a width(opening width) W, the ratio W/L is 0.4.

FIG. 8B shows the DOF characteristic obtained by the mask enhancer 110disposed at the center out of the three mask enhancers 110 with thepattern distance R changed. Similarly to the DOF characteristic shown inFIG. 7B, also in the DOF characteristic shown in FIG. 8B, the DOFcharacteristic is locally improved when the pitch P, namely, the patterndistance R (more accurately, a distance between the phase shifters 112of the adjacent mask enhancers 110) is equal to or approximate toλ/(2×sin φ) (which is approximately 0.20 μm under the conditions for thesimulation). Also, as shown in FIG. 8B, a maximum value of the DOFappears also when the pattern distance R is a value obtained by adding amultiple of λ/(sin φ+NA) (which is approximately 0.18 μm) to λ/(2×sin φ)(which is approximately 0.20 μm).

In other words, when the patterns consisting of the three mask enhancers110 are subjected to the oblique incident exposure, a maximum value ofthe DOF is obtained when the pattern distance R is λ/(2×sin φ) (which isapproximately 0.20 μm). Furthermore, a maximum value of the DOF can beobtained also when the pattern distance R is λ/(2×sin φ)+n×λ/(sin φ+NA)(wherein n is a natural number). This seems to be caused, in the obliqueincident exposure performed on the patterns consisting of the infinitelyperiodically arranged mask enhancers, by a diffraction phenomenon thatphase shifts (phase change) respectively caused in the 0th-orderdiffraction light and the first-order diffraction light are synchronizeddue to the defocus as well as by a phenomenon that images formed by the0th-order diffraction light and the first-order diffraction light areinterfered by higher order diffraction light in the opposite phase.Accordingly, it can be presumed that the aforementioned relationalexpression representing the pattern distance R for obtaining a maximumvalue of the DOF holds in general.

On the basis of the description given so far, the present inventor hasfound that in the case where a pattern including a phase shifter as themask enhancer 110 is used as the main pattern 101 of the photomaskaccording to this embodiment shown in FIG. 1A, the DOF characteristic intransferring the main pattern 101 through the exposure can be largelyimproved by arranging, as the auxiliary patterns 102, patterns that arenot transferred through the exposure but generate diffraction lights(namely, diffraction light generation patterns) in predeterminedpositions. In this case, the predetermined positions are positions awayfrom the center of the phase shifter 101B of the main pattern 101(namely, the phase shifter 112 of the mask enhancer 110) respectively bya distance λ/(2×sin φ) and a distance λ/(2×sin φ)+n×λ/(sin φ+NA)(wherein n is a positive integer). FIGS. 9A through 9C are plan views ofmask patterns according to this invention in each of which diffractionlight generation patterns (auxiliary patterns) are arranged for largelyimproving the DOF characteristic of a main pattern made from a maskenhancer.

As shown in FIG. 9A, first-order diffraction light generation patterns(first auxiliary patterns) 113 (with a width D) made from asemi-shielding portion with a dimension not transferred through exposureare disposed in positions away, by a distance of, for example, λ/(2×sinφ), from the center of a phase shifter 112 (with a width W) of a maskenhancer 110 (with a width L) composed of the phase shifter 112 providedwithin a semi-shielding portion 111. Thus, the DOF characteristic of themask enhancer 110 can be improved.

Also, as shown in FIG. 9B, second-order diffraction light generationpatterns (second auxiliary patterns) 114 (with a width D) made from asemi-shielding portion with a dimension not transferred through exposureare disposed in positions away, by a distance of, for example, λ/(2×sinφ)+λ/(sin φ+NA), from the center of a phase shifter 112 of a maskenhancer 110 composed of the phase shifter 112 provided within asemi-shielding portion 111. Thus, the DOF characteristic of the maskenhancer 110 can be improved.

Furthermore, since the effect to improve the DOF is derived fromdiffraction light, the present inventor has found that the DOFcharacteristic of the mask enhancer 110 can be largely improved bysynthesizing the auxiliary patterns of FIG. 9A and the auxiliarypatterns of FIG. 9B as shown in FIG. 9C. Specifically, the effect toimprove the DOF characteristic can be increased when the first-orderdiffraction light generation patterns 113 are disposed in the positionsaway from the center of the phase shifter 112 of the mask enhancer 110by the distance λ/(2×sin φ) and the second-order diffraction lightgeneration patterns 114 are disposed in the positions away from thecenter of the phase shifter 112 by the distance λ/(2×sin φ)+λ/(sinφ+NA).

In other words, as compared with periodic arrangement where a distance Xfrom the main pattern to the first auxiliary pattern and a distance Yfrom the first auxiliary pattern to the second auxiliary pattern areequal, the DOF characteristic can be more largely improved in theabove-described aperiodic arrangement where the distance X from the mainpattern to the first auxiliary pattern is larger than the distance Yfrom the first auxiliary pattern to the second auxiliary pattern. Inthis case, the optimum ratio X/Y between the distances X and Y isrepresented as (sin φ+NA)/(2×sin φ). When this expression is expressedby using the oblique incident position S that satisfies sin φ=NA×Swherein φ is the oblique incident angle, X/Y=(sin φ+NA)/(2×sinφ)=(1+S)/(2×S). Thus, the ratio can be obtained as a value not dependingupon the NA.

Although not shown in the drawings, a third-order diffraction lightgeneration pattern (third auxiliary pattern) made from a semi-shieldingportion with a dimension not transferred through exposure is preferablydisposed in a position away from the center of the second auxiliarypattern 114 (along a direction away from the mask enhancer 110) by adistance λ/(sin φ+NA). Similarly, fourth, fifth, sixth and higher orderdiffraction light generation patterns made from semi-shielding portionseach with a dimension not transferred through exposure are preferablydisposed, as the auxiliary patterns, in positions away from the centerof the third auxiliary pattern respectively by distances correspondingto multiples of λ/(sin φ+NA).

Now, the effect attained by disposing the diffraction light generationpatterns in the above-described positions will be confirmed throughsimulation.

First, the result of simulation performed by the present inventor forproving that a good DOF characteristic of a main pattern made from amask enhancer can be obtained by disposing diffraction light generationpatterns in positions shown in each of FIG. 9A through 9C will beexplained. FIG. 10A is a diagram of a pattern (mask pattern) used in thesimulation. Specifically, as shown in FIG. 10A, first-order diffractionlight generation patterns (first auxiliary patterns) 113 made from asemi-shielding portion with a dimension not transferred through exposureare disposed in positions away, by a distance X, from the center of aphase shifter 112 of a mask enhancer 110 composed of the phase shifter112 provided within a semi-shielding portion 111. Also, second-orderdiffraction light generation patterns (second auxiliary patterns) 114made from a semi-shielding portion with a dimension not transferredthrough exposure are disposed in positions away, by a distance Y, fromthe centers of the first-order diffraction light generation patterns 113(along directions away from the mask enhancer 113). In this case, themask enhancer 110 has a width L, the phase shifter 112 has a width W andeach of the first-order diffraction light generation patterns 113 andthe second-order diffraction light generation patterns 114 has a widthD. FIG. 10B is a diagram for showing the result of the simulation forthe DOF characteristic obtained by using the pattern of FIG. 10A.Specifically, FIG. 10B is a diagram obtained as follows: The pattern ofFIG. 10A is subjected to the exposure with the distances X and Yvariously changed, so as to obtain, through the simulation, the valuesof the DOF of patterns formed correspondingly to the mask enhancer 110,and the values of the DOF are mapped with respect to the distances X andY. The simulation is performed under the following conditions: L=100 nm;W=60 nm; D=70 nm; the wavelength λ of the light source (ArF lightsource)=193 nm; the lens numerical aperture NA=0.6; and sin φ (wherein φis an oblique incident angle)=0.8×NA. Also, the semi-shielding portionused for forming the first-order diffraction light generation patterns113 and the second-order diffraction light generation patterns 114 hastransmittance of 6%, and a dimension (width) of a pattern to be formedcorrespondingly to the mask enhancer 110 is 100 nm. Furthermore, in FIG.10B, a contour line indicates a DOF, and a point A corresponds to apoint where the distance X=λ/(2×sin φ) (which is approximately 0.20 μm)and the distance Y=λ/(sin φ+NA) (which is approximately 0.18 μm). Asshown in FIG. 10B, a substantially maximum value of the DOF can beobtained at the point A. Specifically, it has been proved that a goodDOF characteristic can be obtained by using the photomask according tothis modification shown in FIG. 4.

Furthermore, the result of simulation performed by the present inventorby using the pattern of FIG. 10A under various optical conditions forproving that a DOF can be maximized by disposing the diffraction lightgeneration patterns in the positions shown in FIG. 4 under arbitraryoptical conditions will be explained.

FIG. 11A is a diagram for showing the result of simulation for the DOFcharacteristic performed under optical conditions that the lensnumerical aperture NA=0.6 and sin φ=0.7×NA (with the other conditionsthe same as those employed in FIG. 10B). In FIG. 11A, a point Acorresponds to a point where the distance X=λ/(2×sin φ) (which isapproximately 0.23 μm) and the distance Y=λ/(sin φ+NA) (which isapproximately 0.19 μm). As shown in FIG. 11A, a substantially maximumvalue of the DOF can be obtained at the point A.

FIG. 11B is a diagram for showing the result of simulation for the DOFcharacteristic performed under optical conditions that the lensnumerical aperture NA=0.6 and sin φ=0.6×NA (with the other conditionsthe same as those employed in FIG. 10B). In FIG. 11B, a point Acorresponds to a point where the distance X=λ/(2×sin φ) (which isapproximately 0.268 μm) and the distance Y=λ/(sin φ+NA) (which isapproximately 0.20 μm). As shown in FIG. 11B, a substantially maximumvalue of the DOF can be obtained at the point A.

FIG. 11C is a diagram for showing the result of simulation for the DOFcharacteristic performed under optical conditions that the lensnumerical aperture NA=0.7 and sin φ=0.7×NA (with the other conditionsthe same as those employed in FIG. 10B). In FIG. 11C, a point Acorresponds to a point where the distance X=λ/(2×sin φ) (which isapproximately 0.196 μm) and the distance Y=λ/(sin φ+NA) (which isapproximately 0.162 μm). As shown in FIG. 11C, a substantially maximumvalue of the DOF can be obtained at the point A.

In the above explanation, the point light sources are used as a premise.Now, the result of simulation performed, by using a light source with anarea, for evaluating the effect of the diffraction light generationpatterns to improve the DOF characteristic will be explained. FIGS. 12Athrough 12C are diagrams of patterns (mask patterns) used in thesimulation.

Specifically, the mask pattern of FIG. 12A consists of a mask enhancer110 with a width L alone. The mask enhancer 110 is composed of asemi-shielding portion 111 in the shape corresponding to the outline ofthe mask enhancer and a phase shifter 112 (with a width W) provided atthe center of the mask enhancer 110 and surrounded by the semi-shieldingportion 111. The mask pattern of FIG. 12B is obtained by adding, to themask enhancer 110 of FIG. 12A, first diffraction light generationpatterns 113 for generating diffraction light that diffracts at an angleθ satisfying sin θ=2×sin φ (wherein φis an oblique incident angle). Inthis case, the first-order diffraction light generation patterns 113 aresemi-shielding patterns and have a width D. The mask pattern of FIG. 12Cis obtained by adding, to the mask enhancer 110 and the first-orderdiffraction light generation patterns 113 of FIG. 12B, second-orderdiffraction light generation patterns 114 for generating diffractionlight that diffracts at an angle η satisfying sin η=2×(NA+sin φ)(wherein φ is an oblique incident angle and NA is lens numericalaperture). In this case, the second-order diffraction light generationpatterns 114 are semi-shielding patterns and have a width D.

FIG. 12D is a diagram of a light source, specifically, an annular lightsource used in the simulation. As shown in FIG. 12D, the annular lightsource has outer and inner diameters of 0.8 and 0.6, respectively(standardized by the lens numerical aperture NA). In this case, when theoblique incident angle is φ, oblique incident light satisfying0.6×NA<sin φ<0.8×NA is present. In this case, it seems that the optimumpositions of the first-order diffraction light generation patterns 113and the second-order diffraction light generation patterns 114 can bedetermined depending upon the oblique incident angle corresponding to aprincipal component of the light source. Specifically, in using theabove-described light source, an average value of the oblique incidentangle φ can be regarded as the principal component of the light source,and hence, the oblique incident angle φ corresponding to the principalcomponent is represented as sin φ=NA×(0.6+0.8)/2=0.7×NA. This and theresult confirmed through the simulation will be continuously explained.

FIG. 12E is a graph for showing the result of simulation for a lightintensity distribution caused correspondingly to each mask enhancerobtained by subjecting each of the mask patterns of FIGS. 12A through12C to the exposure under predetermined conditions. FIG. 12F is adiagram for showing the result of simulation for a defocuscharacteristic of a CD of a pattern with a width of 0.1 μm formedcorrespondingly to each mask enhancer 110 by subjecting each of the maskpatterns of FIGS. 12A through 12C to the exposure under thepredetermined conditions. Herein, a “CD” means a critical dimension,which corresponds to the ultimate dimension of the pattern to be formed.In the simulation, L=180 nm, W=60 nm and D=90 nm, and the positions ofthe diffraction light generation patterns are determined on the basis ofthe oblique incident angle φ that satisfies sin φ=0.7×NA=0.42. Also, thewavelength λ of the light source (ArF light source) is 193 nm, and thelens numerical aperture NA is 0.6. Furthermore, the semi-shieldingportion used for forming the first-order diffraction light generationpatterns 113 and the second-order diffraction light generation patterns114 has transmittance of 6%. In FIGS. 12E and 12F, lines (a), (b) and(c) respectively correspond to the mask patterns shown in FIGS. 12A, 12Band 12C.

As shown in FIG. 12E, images (light intensity distributions) with veryhigh contrast can be formed by all the mask patterns shown in FIGS. 12Athrough 12C, namely, the mask patterns each including the mask enhancer110. Also, a portion in each light intensity distribution related toformation of a pattern of 0.1 μm is minimally affected by thefirst-order diffraction light generation patterns 113 and thesecond-order diffraction light generation patterns 114. In this case,since the critical light intensity in the formation of a pattern of 0.1μm (100 nm) is approximately 0.2, it is understood that the first-orderdiffraction light generation patterns 113 and the second-orderdiffraction light generation patterns 114 are not resolved to betransferred onto a resist.

Also, as shown in FIG. 12F, when the first-order diffraction lightgeneration patterns 113 and the second-order diffraction lightgeneration patterns 114 are added to the mask pattern, the defocuscharacteristic of the mask enhancer 110 can be remarkably improved. Inother words, when the mask enhancer 110 including the phase shifter 112is used together with the first-order diffraction light generationpatterns 113 and the second- order diffraction light generation patterns114, pattern formation with a good defocus characteristic can berealized.

Next, the result of simulation performed by the present inventor forproving that the method for calculating the positions for disposing thediffraction light generation patterns for optimizing the defocuscharacteristic introduced theoretically as described above is correctwill be explained. Specifically, the positions of the diffraction lightgeneration patterns 113 or 114 are changed in the mask pattern of FIG.12B or 12C, so that values of the DOF of a line pattern with a width of0.1 μm formed correspondingly to the mask enhancer 110 can be obtainedthrough the simulation. In this case, the DOF is a defocus range wherethe width of the line pattern is changed from 0.1 μm to 0.09 μm. Also,the simulation conditions are the same as those employed in FIGS. 12Eand 12F.

FIG. 13A is a diagram of the first-order diffraction light generationpatterns 113 disposed in positions away from the center of the phaseshifter 112 by a distance P1 in the mask pattern of FIG. 12B. Also, FIG.13B is a graph for showing the change of the DOF obtained throughexposure performed with the distance P1 changed in the mask pattern ofFIG. 13A. As shown in FIG. 13B, when the distance P1 is approximately230 nm, which is obtained by the theoretical expression λ/(2×sin φ), theDOF has a substantially peak value.

FIG. 13C is a diagram of the second-order diffraction light generationpatterns 114 disposed in positions away from the centers of thefirst-order diffraction light generation patterns 113 by a distance P2in the mask pattern of FIG. 12C. In this case, the distance between thephase shifter 112 and the first-order diffraction light generationpattern 113 is λ/(2×sin φ) (which is approximately 230 nm). Also, FIG.13D is a diagram for showing the change of the DOF obtained through theexposure performed with the distance P2 changed in the mask pattern ofFIG. 13C. As shown in FIG. 13D, when the distance P2 is approximately190 nm, which is obtained by the theoretical expression λ/(sin φ+NA),the DOF has a substantially peak value.

As described so far, in the oblique incident exposure performed on aphase shifter or a mask enhancer by using an aligner having a wavelengthλ of a light source (disposed away from the normal line extendingthrough the center of the lens by a distance S) and lens numericalaperture NA, the DOF characteristic of a pattern to be formedcorrespondingly to the phase shifter or the mask enhancer can beoptimized by disposing diffraction light generation patterns as follows:First-order diffraction light generation patterns are disposed inpositions away from the center of the phase shifter or the mask enhancer(namely, the center of the phase shifter in either case) by a distanceλ/(2×sin φ) and second-order diffraction light generation patterns aredisposed in positions away from the centers of the first-orderdiffraction light generation patterns by a distance λ/(sin φ+NA),namely, away from the center of the phase shifter by a distance λ/(2×sinφ)+λ/(sin φ+NA).

In the above description, the optimum positions for disposingdiffraction light generation patterns with respect to a principalcomponent of the oblique incident angle φ determined depending upon theshape of a light source are described. Subsequently, allowable ranges ofthe positions for disposing the diffraction light generation patternswill be described. As shown in FIG. 8B, there is a position where theDOF is the minimum (hereinafter referred to as the worst position)between the optimum positions of a diffraction light generationpatterns. When it is assumed that an intermediate position between theoptimum position and the worst position is defined as a position wherean average DOF improving effect can be obtained (hereinafter referred toas the average position), the diffraction light generation pattern ispreferably disposed between a pair of average positions sandwiching theoptimum position. Alternatively, the center of the diffraction lightgeneration pattern is more preferably disposed between intermediatepositions between the optimum position and a pair of average positionssandwiching the optimum position.

Specifically, the optimum position of a second-order diffraction lightgeneration pattern is a position away from the center of the phaseshifter by a distance λ/(2×sin φ)+λ/(sin φ+NA). When this position isdesignated as a point OP, worst positions on both sides of the point OPare positions away from and on the both sides of the point OP by adistance (λ/(sin φ+NA))/2. Also, average positions on the both sides ofthe point OP are positions away from and on the both sides of the pointOP by a distance λ/(sin φ+NA))/4. When the second-order diffractionlight generation pattern is preferably disposed in a region sandwichedbetween this pair of average positions, the second-order diffractionlight generation pattern is preferably disposed in a region away fromthe center of the phase shifter by a distance ranging from λ/(2×sinφ)+(λ/(sin φ+NA))×(¾) to λ/(2×sin φ)+(λ/(sin φ+NA))×( 5/4). In the casewhere these expressions are converted into numerical values under thesame conditions as those employed in FIG. 13C, the second-orderdiffraction light generation pattern is preferably disposed in a regionaway from the center of the first-order diffraction light generationpattern by a distance ranging from 143 nm to 238 nm.

Also, intermediate positions between the optimum position of thesecond-order diffraction light generation pattern and a pair of averagepositions sandwiching the optimum position are away from and on the bothsides of the point OP by a distance λ/(sin φ+NA))/8. In this case, it ismost preferred that the second-order diffraction light generationpattern is an auxiliary pattern not for use for forming a resist patternand that the center of the second-order diffraction light generationpattern is disposed between the pair of intermediate positionssandwiching the optimum position. Specifically, the center of thesecond-order diffraction light generation pattern is preferably disposedin a region away from the center of the phase shifter by a distanceranging from λ/(2×sin φ)+(λ/(sin φ+NA))×(⅞) to λ/(2×sin φ)+(λ/(sinφ+NA))×( 9/8). When these expressions are converted into numericalvalues under the same conditions as those employed in FIG. 13C, thecenter of the second-order diffraction light generation pattern ispreferably disposed in a region away from the center of the first-orderdiffraction light generation pattern by a distance ranging from 166 nmto 214 nm.

Similarly to the second-order diffraction light generation pattern, afirst-order diffraction light generation pattern is also preferablydisposed in a region sandwiched between a pair of average positions awayfrom and on both sides of the optimum position of the first-orderdiffraction generation pattern by a distance (λ/(sin φ+NA))/4.Alternatively, the center of the first-order diffraction lightgeneration pattern is preferably disposed in a region sandwiched betweena pair of intermediate positions between the optimum position of thefirst-order diffraction light generation pattern and a pair of averagepositions sandwiching the optimum position, namely, in a regionsandwiched between a pair of intermediate positions away from and on theboth sides of the optimum position of the first-order diffraction lightgeneration pattern by a distance (λ/(sin φ+NA))/8.

Specifically, the first-order diffraction light generation pattern ispreferably disposed in a region away from the center of the phaseshifter by a distance ranging from λ/(2×sin φ)−(λ/(sin φ+NA))/4 toλ/(2×sin φ)+(λ/(sin φ+NA))/4. When these expressions are converted intonumerical values under the same conditions as those employed in FIG.13A, the first-order diffraction light generation pattern is preferablydisposed in a region away from the center of the phase shifter by adistance ranging from 183 nm to 278 nm. Alternatively, the center of thefirst-order diffraction light generation pattern is preferably disposedin a region away from the center of the phase shifter by a distanceranging from λ/(2×sin φ)−(λ/(sin φ+NA))/8 to λ/(2×sin φ)+(λ/(sin φ+NA))/8. When these expressions are converted into numerical values under thesame conditions as those employed in FIG. 13A, the center of thefirst-order diffraction light generation pattern is preferably disposedin a region away from the center of the phase shifter by a distanceranging from 206 nm to 254 nm.

The aforementioned allowable range of the position of the second-orderdiffraction light generation pattern is not applied merely when theauxiliary patterns up to the second-order diffraction light generationpatterns are provided as shown in, for example, FIG. 4. Specifically, inthe case where third-order diffraction light generation patterns,fourth-order diffraction light generation patterns and the like areprovided, the third-order diffraction light generation patterns, thefourth-order diffraction light generation patterns and the like arepreferably disposed in allowable ranges of their positions defined inthe same manner as the second-order diffraction light generationpatterns.

Modification 2 of Embodiment 1

As Modification 2 of Embodiment 1, a preferable range of the obliqueincident angle for the photomask according to Embodiment 1 (orModification 1 of Embodiment 1) will be described. Although thepreferable positions of the auxiliary patterns with respect to anoblique incident angle employed in exposure have been described so far,this modification describes that there actually presents a preferableoblique incident angle. Specifically, a photomask in which auxiliarypatterns are disposed in optimum positions with respect to thepreferable oblique incident angle can exhibit the best pattern formationcharacteristics.

Illumination used in actual exposure is not a point light source but alight source with a given area. Therefore, there are a plurality ofoblique incident angles φ in the exposure. Therefore, in order toconsider a preferable oblique incident angle, light sources used in theoblique incident illumination (off-axis illumination) are classifiedinto a group of annular illumination, a group of dipole illumination anda group of quadrupole illumination for the following reason: In, forexample, the annular illumination, all light components are obliqueincident components for a mask surface but some light components are notsubstantially oblique incident components for each line pattern on themask. In contrast, in the dipole illumination and the quadrupoleillumination, there is no light component other than oblique incidentcomponents.

Specifically, in the annular illumination, light entering from adirection perpendicular to a direction along which a line patternextends (hereinafter referred to as the line direction) is obliqueincident light for the line pattern but light entering from a directionparallel to the line direction is substantially vertical incident lightfor the line pattern. Accordingly, illumination having such a verticalincident component can be classified as the group of the annularillumination regardless of the shape thereof.

On the other hand, in the dipole illumination that is polarized along adirection perpendicular to the line direction, there is substantially novertical incident light component for the line pattern. Therefore,illumination having such oblique incident light components alone can beclassified as the group of the dipole illumination regardless of theshape thereof.

Alternatively, in the quadrupole illumination, there is no lightcomponent entering in a direction parallel to the line direction(namely, substantially vertical incident light component) similarly tothe dipole illumination. Furthermore, the quadrupole illumination hasmerely oblique incident light entering in a diagonal direction to theline direction (namely, a direction at an angle of 45 degrees againstthe line direction). For example, in the case where ight with themaximum oblique incident angle φ_(MAX), which is defined as sinφ_(MAX)=NA with respect to the numerical aperture NA, enters from adiagonal direction at 45 degrees against the line direction, if thislight is projected in a direction perpendicular to the line direction,this light is substantially equivalent to an oblique incident componentsatisfying sin φ=NA×0.5^(0.5). Because of such specificity, thequadrupole illumination has a different property from the dipoleillumination.

Now, the dependency of the DOF on the oblique incident angle obtainedwhen diffraction light generation patterns are disposed as auxiliarypatterns with respect to a main pattern will be described by using theresult of simulation. In this case, the mask patterns of FIGS. 9Athrough 9C are used in the simulation. In the mask pattern of FIG. 9A,the first auxiliary patterns 113 alone are disposed. These firstauxiliary patterns 113 are made from a semi-shielding portion and have awidth D. In the mask pattern of FIG. 9B, the second auxiliary patterns114 alone are disposed. These second auxiliary patterns 114 are alsomade from a semi-shielding portion and have a width D. In the maskpattern of FIG. 9C, both the first auxiliary patterns 113 and the secondauxiliary patterns 114 are disposed. Also, each mask enhancer 110 ofFIGS. 9A through 9C is composed of a semi-shielding portion 111 and aphase shifter 112 and has a mask width L and the phase shifter has awidth W.

FIGS. 14A through 14D show the result of simulation performed throughthe oblique incident exposure carried out on the mask patterns of FIG.9A through 9C by using the annular illumination. FIG. 14A is a diagramof the annular illumination used in the simulation. In FIG. 14A, thelighting shape has an inner diameter S1 and an outer diameter S2. FIG.14A also shows a XY coordinate system. It is herein assumed that eachline pattern of FIGS. 9A through 9C (the mask enhancer 110 and the firstand second auxiliary patterns 113 and 114) is disposed in parallel tothe Y axis of the XY coordinate system. Also, in simulating thedependency of the DOF on the oblique incident angle, in the case wherethe illumination of FIG. 14A is used for the exposure, the obliqueincident position S is defined as (S1+S2)/2, and each of the auxiliarypatterns 113 and 114 of FIGS. 9A through 9C is arranged on the basis ofsin φ=S×NA, so as to simulate the pattern formation characteristics. Inthe simulation, L=100 nm, W=60 nm, D=60 nm, λ=193 nm and NA=0.7. Also,the shape of the annular illumination is determined so that S2−S1=0.02.FIGS. 14B through 14D show the result of the simulation for thedependency of the DOF on the oblique incident angle φ (more precisely,on the oblique incident position S=sin φ/NA) performed under theseconditions for forming a pattern with a width of 80 nm by using each ofthe mask patterns of FIGS. 9A through 9C. In FIGS. 14B through 14D, theresult obtained by using a shielding pattern with a width of 100 nm as amain pattern is also shown for comparison. Specifically, in FIGS. 14Bthrough 14D, the result obtained when the main pattern has the maskenhancer structure is shown with a solid line and the result obtainedwhen the main pattern is a shielding pattern is shown with a brokenline.

In all the results shown in FIGS. 14B through 14D, the DOF obtainedunder an illumination condition that S is approximate to 0.7 is themaximum. Also, under a condition that S is not less than 0.58 and notmore than 0.8, the DOF can be improved by using the mask enhancerstructure as the main pattern as compared with the case where theshielding pattern is used as the main pattern. Specifically, under anexposure condition that the oblique incident angle φ satisfies sinφ=0.7×NA, each of the mask patterns of FIGS. 9A through 9C in which theauxiliary patterns are disposed in the positions defined by using sin φand NA against the main pattern made from the mask enhancer can be amask pattern for realizing the best pattern formation characteristics.Although the optimum illumination condition is defined as describedabove, when the mask enhancer structure is introduced into a mainpattern and illumination condition that sin φ is not less than 0.6×NAand not more than 0.8×NA is employed, the DOF can be improved ascompared with the case where the main pattern is made from a shieldingpattern.

More specific explanation will be given by exemplifying theabove-described conditions for the simulation. Since the optimumillumination condition is sin φ=0.7×NA and NA=0.7, an optimum photomaskcan be obtained by disposing the first auxiliary pattern (moreaccurately, the center thereof) in a position away from the phaseshifter included in the main pattern by a distance λ/(2×sinφ=0.193/(2×0.7×0.7)=197 nm. Similarly, an optimum photomask can beobtained by disposing the second auxiliary pattern (more accurately, thecenter thereof) in a position away from the center of the phase shifterincluded in the main pattern by a distance λ/(2×sin φ)+λ/(NA+sinφ)=0.193/(2×0.7×0.7)+0.193/(0.7+0.7×0.7)=359 nm.

Furthermore, the DOF can be improved when the mask enhancer structure isintroduced into a main pattern and the first auxiliary pattern (moreaccurately, the center thereof) is disposed in a position away from thecenter of the phase shifter of the main pattern by a distance rangingfrom 0.193/(2×0.8×0.7)=172 nm to 0.193/(2×0.58×0.7)=238 nm. Similarly,the DOF can be improved when the second auxiliary pattern (moreaccurately, the center thereof) is disposed in a position away from thecenter of the phase shifter of the main pattern by a distance rangingfrom 0.193/(2×0.8×0.7)+0.193/(0.7+0.8×0.7)=325 nm to0.193/(2×0.58×0.7)+0.193/(0.7+0.58×0.7)=412 nm.

FIGS. 15A through 15D show the result of simulation performed bysubjecting the mask patterns of FIGS. 9A through 9C to the obliqueincident exposure using the dipole illumination. FIG. 15A is a diagramof the dipole illumination used in the simulation. FIG. 15A also showsthe XY coordinate system. In FIG. 15A, the inside coordinate ofpolarized illumination is indicated by x1 and the outside coordinate isindicated by x2. In this case, it is assumed that the polarizationdirection of the dipole illumination is perpendicular to the linedirection of the mask enhancer 110 and the like. Specifically, thepolarization direction of the dipole illumination is parallel to the Xaxis of the XY coordinate system, and each line pattern of FIGS. 9Athrough 9C is arranged in parallel to the Y axis of the XY coordinatesystem. Also, in simulating the dependency of the DOF on the obliqueincident angle, in the case where the illumination of FIG. 15A is usedfor the exposure, the oblique incident position S is defined as(x1+x2)/2, and each of the auxiliary patterns 113 and 114 of FIGS. 9Athrough 9C is arranged on the basis of sin(pφS×NA, so as to simulate thepattern formation characteristics. In the simulation, L==100 nm, W=60nm, D=60 nm, λ=193 nm and NA=0.7. Also, the shape of the dipoleillumination is determined so that x2 −x1=0.02. Similarly to FIGS. 14Bthrough 14D where the annular illumination is used, FIGS. 15B through15D show the result of the simulation for the dependency of the DOF onthe oblique incident angle φ (more precisely, on the oblique incidentposition S=sin φ/NA) performed under these conditions for forming apattern with a width of 80 nm by using each of the mask patterns ofFIGS. 9A through 9C. In FIGS. 15B through 15D, the result obtained byusing a shielding pattern with a width of 100 nm as a main pattern isalso shown for comparison. Specifically, in FIGS. 15B through 15D, theresult obtained when the main pattern has the mask enhancer structure isshown with a solid line and the result obtained when the main pattern isa shielding pattern is shown with a broken line.

In all the results shown in FIGS. 15B through 15D, the DOF obtainedunder an illumination condition that S is approximate to 0.58 is themaximum. Also, under an illumination condition that S is not less than0.5 and not more than 0.7, the DOF can be improved by using the maskenhancer structure as the main pattern as compared with the case wherethe shielding pattern is used as the main pattern. Specifically, underan exposure condition that the oblique incident angle φ satisfies sinφ=0.58×NA, each of the mask patterns of FIGS. 9A through 9C in which theauxiliary patterns are disposed in the positions defined by using sin φand NA against the main pattern made from the mask enhancer can be amask pattern for realizing the best pattern formation characteristics.Although the optimum illumination condition is defined as describedabove, when the mask enhancer structure is introduced into a mainpattern and an illumination condition that sin φ is not less than 0.5×NAand not more than 0.7×NA is employed, the DOF can be improved ascompared with the case where the main pattern is made from a shieldingpattern.

FIGS. 16A through 16D show the result of simulation performed bysubjecting the mask patterns of FIGS. 9A through 9C to the obliqueincident exposure using the quadrupole illumination. FIG. 16A is adiagram of the quadrupole illumination used in the simulation. FIG. 16Aalso shows the XY coordinate system. Each line pattern (the maskenhancer 110 and the first and second auxiliary patterns 113 and 114) ofFIGS. 9A through 9C is disposed in parallel to the Y axis of the XYcoordinate system. The quadrupole illumination of FIG. 16A is polarizedin diagonal directions against the direction of the line pattern (theline direction) and the inside coordinate of the polarized illuminationalong a direction (the X axis direction) perpendicular to the linedirection (the Y axis direction) is indicated by x1 and the outsidecoordinate is indicated by x2. Also, in simulating the dependency of theDOF on the oblique incident angle, in the case where the illumination ofFIG. 16A is used for the exposure, the oblique incident position S isdefined as (x1+x2)/2, and each of the auxiliary patterns 113 and 114 ofFIGS. 9A through 9C is disposed on the basis of sin φ=S×NA, so as tosimulate the pattern formation characteristics. In the simulation, L=100nm, W=60 nm, D=60 nm, λ=193 nm and NA=0.7. Also, the shape of thequadrupole illumination is determined so that x2−x1=0.02. Similarly toFIGS. 15B through 15D where the dipole illumination is used, FIGS. 16Bthrough 16D show the result of the simulation for the dependency of theDOF on the oblique incident angle φ (more precisely, on the obliqueincident position S=sin φ/NA) performed under these conditions forforming a pattern with a width of 80 nm by using each of the maskpatterns of FIGS. 9A through 9C. In FIGS. 16B through 16D, the resultobtained by using a shielding pattern with a width of 100 nm as a mainpattern is also shown for comparison. Specifically, in FIGS. 16B through16D, the result obtained when the main pattern has the mask enhancerstructure is shown with a solid line and the result obtained when themain pattern is a shielding pattern is shown with a broken line.

In all the results shown in FIGS. 16B through 16D, namely, in using thequadrupole illumination, the DOF obtained under an illuminationcondition that S is approximate to 0.50 is the maximum. Specifically, inusing the quadrupole illumination, the optimum oblique incident angle φis defined as sin φ=0.50×NA. Since a position projected onto the X axisof the quadrupole illumination is obtained by multiplying the originalincident position by 0.5^(0.5), this optimum oblique incident anglecorresponds to a value obtained by multiplying the optimum condition inusing the annular illumination, that is, sin φ=0.7, by 0.5^(0.5). Also,the preferable oblique incident angle φ is defined as 0.4×NA≦sinφ≦0.6×NA. In this case, the distance from the center of the light source(the origin of the XY coordinate) to each of the four polarized lightingareas is not less than 0.4/(0.5^(0.5))×NA and not more than0.6/(0.5^(0.5))×NA.

As described above, in using the annular illumination, the preferableoblique incident position S is not less than 0.6 and not more than 0.8,and the optimum value can be obtained under the condition of S=0.7,i.e., sin φ=0.7×NA. In using the dipole illumination, the preferableoblique incident position S is not less than 0.5 and not more than 0.7,and the optimum value can be obtained under the condition of S=0.58,namely, sin φ=0.58×NA. In using the quadrupole illumination, thepreferable oblique incident position S is not less than 0.4 and not morethan 0.6, and the optimum value can be obtained under the condition ofS=0.5, namely, sin φ=0.5×NA. Specifically, between the annularillumination and the dipole illumination, the ranges of the preferableoblique incident position S partly overlap, and hence, any of the maskpatterns of FIGS. 9A through 9C in which the oblique incident position Sis defined as a value not less than 0.58 and not more than 0.7 can be amask pattern for attaining a good DOF characteristic in using anyillumination belonging to the groups of the annular illumination and thedipole illumination. Also, deformed quadrupole illumination, which isdifferent from the ideal quadrupole illumination shown in FIG. 16A andhas lighting areas distributed along larger angular directions notlimited to the angle of 45 degrees against the line direction,substantially belongs to the groups of the annular illumination and thedipole illumination. Therefore, a photomask formed so as to correspondto a preferable oblique incident angle for both the annular illuminationand the dipole illumination can be the most preferable photomask forpractical use.

Furthermore, a photomask formed so as to correspond to the obliqueincident position S of 0.4 or more and 0.8 or less can exhibit a goodDOF characteristic when the illumination conditions are adjustedsuitably to the photomask.

It is noted that the most practically preferable illumination is theannular illumination for the following reason: Since the dipoleillumination exhibits a minimum effect on a line pattern in parallel tothe polarization direction of the lighting shape, patterns suitablyapplicable to the dipole illumination are limited. Since the quadrupoleillumination may cause an unwanted phenomenon that in forming a T-shapedor L-shaped pattern obtained by bending one line, the shape of thepattern can be largely deformed as compared with a mask shape.

Modification 3 of Embodiment 1

As Modification 3 of Embodiment 1, arrangement of the auxiliary patternsfor allowing the mask enhancer structure of the photomask according toEmbodiment 1 (or Modification 1 or 2 of Embodiment 1) to exhibit morepreferable effects will be described.

It has been described so far that various effects can be attained byintroducing the mask enhancer structure to a main pattern. In otherwords, in the mask enhancer structure, the pattern formationcharacteristics such as the DOF and the contrast can be improved bycontrolling the mask width of the main pattern and the width of a phaseshifter provided within the main pattern.

However, in employing any of the structures shown in FIGS. 1B, 1C and 2Athrough 2D, a part of the semi-shielding portion or the shieldingportion surrounding the phase shifter preferably has a given width. Thisis because, when the part of the semi-shielding portion or the shieldingportion surrounding the phase shifter is too fine, such a fine part isdifficult to process in the mask processing, and in post-processing suchas cleaning performed after the processing, there arises a problem of,for example, peeling of the pattern. Also, when the transmittance of thephase shifter is as high as the transmittance of a transparent portion,the phase shifter cannot be distinguished from the transparent portionin a mask inspection utilizing permeability of light. In contrast, whenthere is a semi-shielding portion with low transmittance or a shieldingportion that can be identified by a mask inspection apparatus in theboundary between the phase shifter and the transparent portion, thephotomask can be easily inspected.

From the viewpoint of the mask processing, the width of the part of thesemi-shielding portion or the shielding portion surrounding the phaseshifter is preferably at least 20 nm (in the actual dimension on thephotomask) in the mask enhancer structure. This is because theresolution limit attained by utilizing a technique of twice exposure inan electron beam aligner used in the photomask processing isapproximately 20 nm.

Furthermore, the mask inspection is ideally performed by using light ofthe same wavelength as the exposure wavelength, and therefore, adimension that can be identified by the mask inspection apparatus ispreferably not less than ¼ times as large as the exposure wavelength (inthe actual dimension on the photomask). This is because a smallerdimension cannot be identified by using light. Herein, the actualdimension on the photomask means the actual dimension of a part formedon the photomask not converted by using the mask magnification.

However, in order to obtain the effects of the mask enhancer, lightpassing through the phase shifter and light passing through thetransparent portion should interfere with each other, and therefore, thedimension of the part of the semi-shielding portion (or the shieldingportion) sandwiched between the phase shifter and the transparentportion is preferably not more than 0.3×λ/NA, that is, a distance atwhich the two lights can strongly interfere with each other. This is,however, a distance on a transferred image on the wafer, and therefore,the dimension on the mask is preferably not more than (0.3×λ/NA)×M,which is obtained by multiplying the dimension by the mask magnificationM.

Now, it will be described on the basis of the result of simulation thatgood pattern formation characteristics can be realized by using the maskenhancer structure for exhibiting preferable effects owing to thearrangement of auxiliary patterns according to this modification.

FIG. 17A is a diagram of a mask pattern used in the simulation. In FIG.17A, like reference numerals are used to refer to like elements used inthe photomask of Embodiment 1 shown in FIG. 1A so as to omit detaileddescription.

As shown in FIG. 17A, in a main pattern 101 having the mask enhancerstructure composed of a shielding portion 101A (the first semi-shieldingportion 101A in Embodiment 1) and a phase shifter 101B, the main pattern101 has a width L and the phase shifter 101B has a width W. On bothsides of the main pattern 101, a pair of auxiliary patterns 102 thatdiffract exposing light and are not transferred through exposure areprovided. In this case, the distance between the center of the phaseshifter 101B and the center of the auxiliary pattern 102 is G. Also, theauxiliary pattern 102 is made from a semi-shielding portion with a widthD.

FIGS. 17B through 17D show the result of simulation performed forevaluating the DOF and the exposure margin obtained in forming a patternwith a width of 90 nm while changing the width W and the distance G whenL=90 nm and D=70 nm. Herein, the exposure margin means the ratio (%) ofchange of the exposure energy (dose) necessary for changing a patterndimension by 10%. In other words, as the exposure margin is larger, apattern dimension is more stable against the change of the exposureenergy, and hence preferably, is less changed against the change of theexposure energy in actual pattern formation. In the simulation, λ=193 nmand NA=0.7, and the quadrupole illumination shown in FIG. 16A is used,whereas x1 is 0.45×NA and x2 is 0.6×NA in FIG. 16A.

Specifically, FIG. 17B shows the dependency of the DOF on the width W(of the phase shifter) obtained in the cases where G=240 nm and G=500nm. Also, FIG. 17C shows the dependency of the exposure margin on thewidth W (of the phase shifter) obtained in the cases where G=240 nm andG=500 nm.

As is understood from FIGS. 17B and 17C, in the simulation resultobtained when G=500 nm, both the DOF and the exposure margin are themaximum when the width W is approximate to 90 nm, namely, the width W ofthe phase shifter is substantially equal to the width L of the maskpattern (namely, the width of the main pattern 101). Also, since the DOFmerely gently increases in proportion to the width W of the phaseshifter, when the width W of the phase shifter is small as compared withthe width L of the mask pattern, a sufficient margin cannot be obtained.

In order to obtain a sufficient margin in the pattern formation, it isnecessary to set the width W of the phase shifter to be substantiallyequal to the width L of the mask pattern. However, in this case, thewidth of the part of the shielding portion surrounding the phase shifteris very small, which is not preferable as the mask enhancer structure.

On the other hand, as is understood from FIGS. 17B and 17C, in thesimulation result obtained when G=240 nm, when the width W isapproximate to 60 nm, the exposure margin is the maximum and the DOF issufficiently improved as compared with that attained by a simpleshielding pattern with the width W of 0. Accordingly, when the width Wof the phase shifter is smaller by approximately 30 nm than the width Lof the mask pattern, a sufficient margin can be obtained in the patternformation. In this case, the width of the part of the shielding portionsurrounding the phase shifter is 15 nm. When this is converted into theactual dimension on the mask by assuming the magnification (reductionratio) M is 4-fold, the actual dimension on the mask is 60 nm, andhence, a dimension not less than ¼ of the exposure wavelength (193 nm)can be secured. In FIGS. 17B and 17C, the width W of 90 nm means thatthe main pattern 101 is composed of the phase shifter alone.

It is understood from the aforementioned simulation result that when themain pattern has the same mask width, the exposure margin of thephotomask can be more improved by using auxiliary patterns when the mainpattern has the mask enhancer structure than when the main pattern ismade from a simple phase shifter. When NA×sin φ=(x1+x2)/2, the width Gof 240 nm corresponds to the optimum position of the first auxiliarypattern (auxiliary pattern 102), that is, λ/(2×sin φ). Although hereinnot described in detail, the present inventor has confirmed that asimilar result can be obtained with respect to the second auxiliarypattern (in the case where the width G is 440 nm corresponding to itsoptimum position, λ/(2×sin φ)+λ/(NA+sin φ)).

Furthermore, as is understood from FIGS. 17B and 17C, the exposuremargin abruptly increases in proportion to the width W of the phaseshifter until it becomes the maximum value. On the other hand, if asufficient exposure margin can be secured, the width W of the phaseshifter is not necessarily set to a value for maximizing the exposuremargin. Accordingly, whether or not a sufficient margin can be securedin the pattern formation while sufficiently securing the width of thepart of the semi-shielding or shielding portion surrounding the phaseshifter depends upon whether or not the DOF is largely improved inaccordance with the increase of the width W of the phase shifter in themask enhancer structure.

FIG. 17D shows the result obtained by plotting the dependency of the DOFon a matrix of the width W of the phase shifter and the distance Gbetween the center of the phase shifter and the center of the auxiliarypattern. It is understood from this result that the DOF is abruptlyimproved in proportion to the width W when G=240 nm (0.24 μm) and G=440nm (0.44 μm). These distances G correspond to the optimum position ofthe first auxiliary pattern and the optimum position of the secondauxiliary pattern in this modification as described above. Accordingly,when the auxiliary patterns are disposed in these positions, asufficient margin can be secured in the pattern formation whilesufficiently securing the width of the part of the semi-shieldingportion or the shielding portion surrounding the phase shifter in themask enhancer structure.

Modification 4 of Embodiment 1

As Modification 4 of Embodiment 1, the width of an auxiliary pattern forallowing the photomask according to Embodiment 1 (or Modification 1, 2or 3 of Embodiment 1) to exhibit more preferable effects will bedescribed.

First, the result of simulation for dependency of the DOF and theexposure margin on the width of an auxiliary pattern obtained insubjecting the mask pattern of FIG. 4 to the exposure will be described.In the simulation, λ=193 nm and NA=0.7, and annular illumination (withan inner diameter of 0.65 and an outer diameter of 0.75) is used. Also,it is assumed that a transparent portion and a phase shifter havetransmittance of 1 and that a mask pattern excluding the phase shifteris made from a semi-shielding portion (with transmittance of 6%).Furthermore, the respective auxiliary patterns are disposed in theiroptimum positions as shown in FIG. 4 in accordance with sin φ=0.7×NA.

In general, when the auxiliary pattern is thicker, the DOF of the mainpattern is increased while the exposure margin is reduced. Therefore,the DOF and the exposure margin in transferring a main pattern aresimulated so as to find how this phenomenon actually depends upon thewidths of the first and second auxiliary patterns. Specifically, themain pattern 101 in which the width L is 140 nm and the width W is 80 nmis subjected to the exposure with the widths D1 and D2 of the first andsecond auxiliary patterns 102 and 103 changed from 40 nm to 100 nm, soas to obtain the DOF and the exposure margin.

FIGS. 18A and 18B show the result of the simulation for the DOF and theexposure margin obtained by fixing the width D2 to 70 nm and changingthe width D1 from 40 nm to 100 nm. FIGS. 18C and 18D show the result ofthe simulation for the DOF and the exposure margin obtained with thewidth D1 fixed to 70 nm and the width D2 changed from 40 nm to 100 nm.The DOF and the exposure margin shown in FIGS. 18A through 18D areobtained in forming a pattern with a width of 90 nm.

It is understood from the result shown in FIGS. 18A and 18B that the DOFobtained in transferring the main pattern is largely increased as thewidth D1 of the first auxiliary pattern 102 is increased. On the otherhand, it is understood that the exposure margin obtained in transferringthe main pattern is largely reduced as the width D1 is increased. Inother words, when the first auxiliary pattern 102 is thicker, theexposure margin is reduced although the DOF is improved. Therefore, theexposure margin can be improved merely through trade-off of thesefactors.

On the other hand, as is understood from the result shown in FIGS. 18Cand 18D, the DOF obtained in transferring the main pattern is largelyincreased as the width D2 of the second auxiliary pattern 103 isincreased in the same manner as in the case of the first auxiliarypattern 102. However, even when the width D2 is increased, the exposuremargin obtained in transferring the main pattern is merely slightlyreduced. Therefore, when the width D2 is increased, the DOF can beimproved without reducing the exposure margin.

As described so far, when the width D2 of the second auxiliary patternis larger than the width D1 of the first auxiliary pattern, the DOF canbe improved while keeping a large exposure margin. Furthermore, thepresent inventor has experimentally found that the second auxiliarypattern does not form an unexposed portion on a resist even when thesecond auxiliary pattern has a width approximately 1.2 times as large asthe maximum width of the first auxiliary pattern for avoiding formationof an unexposed portion on the resist. Accordingly, even when the secondauxiliary pattern has a width 1.2 times as large as that of the firstauxiliary pattern, a phenomenon that an unexposed portion is formed in aresist can be avoided. Accordingly, when the width D2 of the secondauxiliary pattern is not less than 1.2 times as large as the width D1 ofthe first auxiliary pattern, the aforementioned effects can bedefinitely attained while preventing the second auxiliary pattern fromforming an unexposed portion in a resist. However, in order to obtainthe effect to improve the DOF by the auxiliary patterns, each auxiliarypattern preferably has a width a half as large as the minimum dimensionat which the auxiliary pattern is resolved. Specifically, when the widthD1 of the first auxiliary pattern is sufficiently large for attainingthe effect to improve the DOF, in order to prevent the second auxiliarypattern from being resolved, the width D2 of the second auxiliarypattern is preferably not more than twice as large as the width D1 ofthe first auxiliary pattern.

In this modification, a pair of auxiliary patterns working as thediffraction light generation patterns are provided on both sides of themain pattern as a premise. However, in the case where a main pattern isdisposed in the vicinity of one side of another main pattern, anauxiliary pattern may be provided merely on the other opposite side ofthe main pattern.

Embodiment 2

A photomask according to Embodiment 2 of the invention will now bedescribed with reference to the accompanying drawing.

FIG. 19 is a plan view of the photomask of Embodiment 2.

As shown in FIG. 19, a main pattern 201 to be transferred throughexposure is provided on a transparent substrate 200. The main pattern201 is composed of a first semi-shielding portion 201A having firsttransmittance for partially transmitting exposing light and a phaseshifter 201B. The first semi-shielding portion 201A is in the shapecorresponding to the outline of the main pattern 201. The phase shifter201B is provided in a peripheral portion of the main pattern 201 so asto be surrounded by a part of the first semi-shielding portion 201A. Thephase shifter 201B is formed by, for example, trenching the transparentsubstrate 200. Each of first auxiliary patterns 202 (with a width D1)that diffract the exposing light and are not transferred through theexposure is provided on the transparent substrate 200 in a position awayfrom the center of the phase shifter 201B of the main pattern 201 by adistance λ/(2×sin φ) so as to sandwich a transparent portion between themain pattern 201 and the first auxiliary pattern 202. Also, each ofsecond auxiliary patterns 203 (with a width D2) that diffract theexposing light and are not transferred through the exposure is providedon the transparent substrate 200 in a position away from the center ofthe first auxiliary pattern 202 (in a direction away from the mainpattern 201) by a distance λ/(NA+sin φ) so as to sandwich a transparentportion between the first auxiliary pattern 202 and the second auxiliarypattern 203. In this case, each of the first auxiliary patterns 202 andthe second auxiliary patterns 203 is made from a second semi-shieldingportion having second transmittance for partially transmitting theexposing light.

In this embodiment, the distance between the phase shifter 201B and thefirst auxiliary pattern 202 may be approximate to λ/(2×sin φ) (seeModification 1 of Embodiment 1).

Also in this embodiment, the distance between the phase shifter 201B andthe second auxiliary pattern 203 may be approximate to λ/(2×sinφ)+λ/(NA+sin φ) (see Modification 1 of Embodiment 1).

Furthermore, in this embodiment, sin φ (wherein φ is an oblique incidentangle) is preferably not less than 0.40×NA and not more than 0.80×NA,and more preferably not less than 0.58×NA and not more than 0.70×NA. Inthe case where the exposure is performed by using annular illumination,sin(p is preferably not less than 0.60×NA and not more than 0.80×NA. Inthe case where the exposure is performed by using quadrupoleillumination, sin φ is preferably not less than 0.40×NA and not morethan 0.60×NA (see Modification 2 of Embodiment 1).

Also, in this embodiment, the width D2 of the second auxiliary pattern203 is preferably larger than the width D1 of the first auxiliarypattern 202. In particular, the width D2 is preferably not less than 1.2times as large as the width D1 (see Modification 4 of Embodiment 1).

Now, a characteristic of the arrangement of the phase shifter in thisembodiment will be described. In the case where the dimension of apattern to be formed is 0.3×λ/NA or less, the phase shifter ispreferably disposed at the center of a semi-shielding portion (asemi-shielding pattern) corresponding to the pattern to be formed.Alternatively, in the case where the dimension of a pattern to be formedis λ/NA or more, the phase shifter is preferably disposed in aperipheral portion of a semi-shielding pattern corresponding to thepattern to be formed. Alternatively, in the case where the dimension ofa pattern to be formed is larger than 0.3×λ/NA and smaller than λ/NA,the phase shifter may be disposed at the center or in a peripheralportion of a semi-shielding pattern corresponding to the pattern to beformed.

The phase shifter is disposed in the peripheral portion of a maskpattern used for forming a pattern with a dimension of λ/NA or more inorder to attain an effect to prove the pattern formation characteristicsby an “outline enhancement method” described later as well as to providediffraction light generation patterns in optimum positions.Specifically, the phase shifter is preferably disposed in a positionaway from the outer periphery of the semi-shielding pattern by adistance λ/(2×sin φ) or less. This is because the phase shifter shouldbe present in a position away from the outer periphery of thesemi-shielding pattern (main pattern) by the distance λ/(2×sin φ) orless in order to dispose first-order diffraction light generationpatterns. Also, in considering that the maximum value of sin φ is NA,when the semi-shielding pattern has a dimension of λ/NA or more, thephase shifter is preferably disposed in the peripheral portion thereof.

In the photomask shown in FIG. 19, a mask pattern consists of the mainpattern 201, the first auxiliary patterns 202 and the second auxiliarypatterns 203. Also, an area on the transparent substrate 200 where themask pattern is not formed corresponds to a transparent portion(opening).

There is a relationship of opposite phases between light passing throughthe phase shifter 201B and light passing through the transparent portion(specifically, a relationship that a phase difference between theselights is not less than (150+360×n) degrees and not more than (210+360×n) degrees (wherein n is an integer)).

Also, there is a relationship of the identical phase between lightpassing through each of the first semi-shielding portion 201A and thesecond semi-shielding portion (namely, the first and second auxiliarypatterns 202 and 203) and light passing through the transparent portion(specifically, a relationship that a phase difference between theselights is not less than (−30+360×n) degrees and not more than (30+360×n)degrees (wherein n is an integer)).

According to Embodiment 2, since the main pattern 201 is composed of thefirst semi-shielding portion 201A and the phase shifter 201B, lightspassing through the transparent portion and the first semi-shieldingportion 201A can be partially cancelled by light passing through thephase shifter 201B. Therefore, the contrast in a light intensitydistribution of a shielded image corresponding to the main pattern 201can be emphasized.

Furthermore, according to Embodiment 2, the first and second auxiliarypatterns 202 and 203 having low transmittance are provided separatelyfrom the main pattern 201. Specifically, the first auxiliary patterns(first-order diffraction light generation patterns) 202 are disposed inpositions away from the center of the phase shifter 201B of the mainpattern 201 by a distance λ/(2×sin φ). Also, the second auxiliarypatterns (second-order diffraction light generation patterns) 203 aredisposed in positions away from the centers of the first auxiliarypatterns 202 by a distance λ/(NA+sin φ). Therefore, diffraction lightfor interfering with the light passing through the phase shifter 201B ofthe main pattern 201 can be definitely generated. Accordingly, thedefocus characteristic of a transferred image of the main pattern 201can be improved, resulting in improving the DOF characteristic.

Even when the distance between the phase shifter 201B and the firstauxiliary pattern 202 is approximate to λ/(2×sin φ) in this embodiment,the above-described effects can be attained to some extent. Similarly,even when the distance between the phase shifter 201B and the secondauxiliary pattern 203 is approximate to λ/(2×sin φ))+λ/(NA +sin φ), theabove-described effects can be attained to some extent (see Modification1 of Embodiment 1). Furthermore, sin φ (wherein φ is an oblique incidentangle) is preferably not less than 0.40×NA and not more than 0.80×NA,and more preferably not less than 0.60×NA and not more than 0.70×NA (seeModification 2 of Embodiment 1).

Moreover, in this embodiment, the width of the part of thesemi-shielding portion (the first semi-shielding portion 201A) of themain pattern 201 sandwiched between the phase shifter 201B and thetransparent portion is preferably at least 20 nm (in the actualdimension on the mask), and more preferably not less than ¼ of exposurewavelength (see Modification 3 of Embodiment 1).

Also, in this embodiment, the width D2 of the second auxiliary pattern203 is preferably larger than the width D1 of the first auxiliarypattern 202. In particular, the width D2 is preferably not less than 1.2times as large as the width D1 (see Modification 4 of Embodiment 1).

Furthermore, according to Embodiment 2, since the first and secondauxiliary patterns 202 and 203 are made from the semi-shielding portion,the degree of freedom in the arrangement of the auxiliary patterns canbe increased. Therefore, the periodicity in the arrangement of thepatterns including the main pattern 201 can be increased, so that theDOF characteristic can be further improved. Also, since the first andsecond auxiliary patterns 202 and 203 are made from the semi-shieldingportion, these auxiliary patterns can be made thick under restrictionthey are not transferred through the exposure, and hence, the auxiliarypatterns can be easily processed.

Moreover, according to Embodiment 2, since the phase shifter 201B isdisposed in the peripheral portion of the main pattern 201, the contrastin the light intensity distribution in an image formed by the lightpassing through the transparent portion in the vicinity of the mainpattern 201 can be emphasized, so that the pattern formation can becarried out while keeping a good defocus characteristic.

Furthermore, according to Embodiment 2, since the phase shifter 201B isformed by trenching the transparent substrate 200, a very good defocuscharacteristic can be exhibited in the pattern formation.

Also in Embodiment 2, either of the first auxiliary patterns 202 and thesecond auxiliary patterns 203 may be omitted.

In Embodiment 2, the first transmittance of the first semi-shieldingportion 201A used for forming the main pattern 201 is preferably 15% orless. Thus, the thickness of a resist film can be prevented fromreducing or the resist sensitivity can be optimized in the patternformation. However, in order to attain such an effect as well as theeffects to improve the DOF and the contrast, the first transmittance ispreferably 3% or more.

Also in Embodiment 2, the second transmittance of the first and secondauxiliary patterns 202 and 203 (namely, the second semi-shieldingportion) is preferably not less than 6% and not more than 50%. Thus, theeffect to improve the DOF derived from the diffraction light can bedefinitely realized while preventing an unexposed portion from beingformed in a resist due to a too high shielding property of the auxiliarypattern.

In Embodiment 2, the first semi-shielding portion 201A and the secondsemi-shielding portion working as the first and second auxiliarypatterns 202 and 203 may be made from one semi-shielding film, such as ametal thin film formed on the transparent substrate 200. In this case,the photomask can be easily processed because each semi-shieldingportion can be easily formed. As the metal thin film, a thin film (witha thickness of approximately 50 nm or less) of Cr (chromium), Ta(tantalum), Zr (zirconium), Mo (molybdenum), or Ti (titanium), or analloy of any of these metals can be used. Examples of the alloy areTa—Cr alloy, Zr—Si alloy, Mo—Si alloy and Ti—Si alloy. Alternatively, athick film including a silicon oxide, such as ZrSiO, CrAIO, TaSiO, MoSiOor TiSiO, may be used instead of the metal thin film.

Furthermore, in Embodiment 2, the phase shifter 201B may be formed byforming, on the transparent substrate 200, a phase shift film made froma material with high transmittance.

Next, a method, found by the present inventor, for improving theresolution of an isolated space pattern by using a structure in which aphase shifter (the phase shifter 201B) is provided in a peripheralportion of a shielding pattern (the main pattern 201) (hereinafterreferred to as the outline enhancement method) will be described. The“outline enhancement method” is based on a principle applicable to anyfine space pattern used in the positive resist process regardless of theshape of the pattern. The following description is given by exemplifyingthe case where a contact pattern is to be formed through the positiveresist process, whereas the outline enhancement method is applicablealso to the negative resist process by replacing a fine space pattern (aresist removal pattern) of the positive resist process with a finepattern (a resist pattern). In the following description, a shieldingpattern excluding a phase shifter is made from a semi-shielding portionunless otherwise mentioned.

In a photomask in which a shielding pattern is provided, for example, soas to surround an opening and a phase shifter is provided in aperipheral portion of the shielding pattern (hereinafter referred to asthe outline enhanced mask), light passing through the phase shifterprovided in the peripheral portion of the shielding pattern, namely,provided around the opening (transparent portion), can partially cancellights passing through the opening and a semi-shielding portion.Accordingly, when the intensity of the light passing through the phaseshifter is controlled to cancel light passing through a region aroundthe opening (an outline region), a light intensity distribution in whichthe light intensity in the outline region is reduced to substantially 0(zero) can be formed. Also, the light passing through the phase shifterstrongly cancels the light passing through the outline region but weaklycancels light passing a region in the vicinity of the center of theopening. As a result, in the light intensity distribution of the lightpassing through the outline enhanced mask, the gradient of the profilefrom the opening to its periphery can be increased. Accordingly, theintensity distribution of the light passing through the outline enhancedmask has a sharp profile, resulting in forming an image of the lightintensity with high contrast. This is the principle that an image of thelight intensity can be emphasized by the outline enhancement method.Specifically, when the phase shifter is provided in the vicinity of theopening in the mask pattern made from a semi-shielding portion with lowtransmittance, a very strong dark part corresponding to the outline ofthe opening can be formed in an image of the light intensity formed byusing the photomask. In this manner, a light intensity distributionhaving emphasized contrast between the light intensity obtained in theopening and the light intensity obtained in the region around theopening can be formed.

It is noted that the semi-shielding portion used in the outlineenhancement method preferably has high transmittance. However, sincetransmitted light may reach a region that should originally be ashielded part due to the presence of the semi-shielding portion, themaximum value of the transmittance of the semi-shielding portion ispreferably approximately 15% in order to, for example, prevent thethickness of a resist film (a resist pattern corresponding to thesemi-shielding portion) from reducing or to optimize the resistsensitivity in the pattern formation. On the other hand, in order toattain the effect of the outline enhancement method, the minimum valueof the transmittance of the semi-shielding portion is preferablyapproximately 3%. Accordingly, the optimum value of the transmittance ofthe semi-shielding portion of the outline enhanced mask is not less than3% and not more than 15%. Also, in the outline enhanced mask, the phaseshifter may be provided in contact with the opening or with a part ofthe semi-shielding portion sandwiched between the phase shifter and theopening. Furthermore, the phase shifter may be provided along the wholeoutline of the opening or along merely part of the outline.

Furthermore, when a semi-shielding pattern for transmitting light in theidentical phase with respect to a transparent portion is used as theshielding pattern, a mask pattern simultaneously employing the centerline enhancement method (described in Embodiment 1) and the outlineenhancement method can be formed. Specifically, a phase shifter isprovided at the center of a semi-shielding pattern used for forming afine line pattern. On the other hand, a phase shifter is provided in aperipheral portion of a semi-shielding pattern used for forming a largepattern. In this manner, the contrast of a light intensity imagecorresponding to the edge of the large pattern can be improved owing tothe outline enhancement method, and therefore, the contrast of the lightintensity image can be emphasized over every part of the whole patternto be formed. Thus, a semi-shielding pattern (a semi-shielding portionfor transmitting light in the identical phase with respect to atransparent portion), which is conventionally not preferably used in amask pattern for use in the pattern formation, can be used for forming apattern in an arbitrary shape. Furthermore, the use of a semi-shieldingpattern, namely, a semi-shielding film, can result in the followingmerits: In a conventional mask, it is necessary to use a thick metalfilm as a mask pattern for securing a sufficient shielding property. Incontrast, a semi-shielding pattern can be made from a thin metal filmwith a semi-shielding property, in other words, the thickness of a metalfilm used for forming the mask pattern can be reduced, the photomask canbe easily processed. Specifically, when a Cr film is used, a thicknessof approximately 100 nm is necessary as a mask pattern in a conventionalmask, but a thickness of approximately 10 nm is sufficient as asemi-shielding pattern. Therefore, even when a fine mask pattern isformed through etching or when cleaning is performed after forming amask pattern, defectives such as peeling can be avoided.

In Embodiment 2, the defocus characteristic (the DOF characteristic) inthe pattern formation can be improved by generating, by using thediffraction light generation patterns (the first and second auxiliarypatterns 202 and 203), diffraction light for interfering with lightpassing through the opening (the phase shifter 201B) provided within themask enhancer (the main pattern 201) for the same reason as thatdescribed in Embodiment 1.

Specifically, in the mask enhancer structure (shown in FIG. 19) for theoutline enhancement method in which a phase shifter (the phase shifter201B) is provided in a peripheral portion of a semi-shielding portion(the first semi-shielding portion 201A), a part of the semi-shieldingportion surrounded by the phase shifter transmits merely light thatcannot sensitize a resist but is optically identical to a transparentportion. Accordingly, the phase shifter of the outline enhancementmethod exhibits the same function as the phase shifter of the centerline enhancement method. Therefore, in the same manner as in the centerline enhancement method, the defocus characteristic can be improved bydisposing a first-order diffraction light generation pattern in aposition away from the center of the phase shifter by a distanceλ/(2×sin φ) and (or) a second-order diffraction light generation patternin a position away from the center of the first-order diffraction lightgeneration pattern by a distance λ/(NA+sin φ). The allowable ranges ofthe positions of the diffraction light generation patterns on the basisof the position of the phase shifter are the same as those employed inthe center line enhancement method described in Embodiment 1.

Embodiment 3

A photomask according to Embodiment 3 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 20A is a plan view of the photomask of Embodiment 3, and FIG. 20Bis a cross-sectional view thereof taken along line XX-XX of FIG. 20A.Also, FIGS. 21A through 21C are cross-sectional views for showingvariations of the cross-sectional structure taken on line XX-XX of FIG.20A.

As shown in FIGS. 20A and 20B, a line-shaped main pattern 301 to betransferred through exposure is provided on a transparent substrate 300.The main pattern 301 is composed of a first shielding portion 301A and aphase shifter 301B. The first shielding portion 301A is formed so as tosurround the phase shifter 301B in a line shape. In other words, thephase shifter 301B is provided at the center of the main pattern 301.The phase shifter 301B is formed by, for example, trenching thetransparent substrate 300. A pair of auxiliary patterns 302 thatdiffract exposing light and are not transferred through the exposure areprovided on the transparent substrate 300 on both sides of the mainpattern 301 so as to sandwich a transparent portion between the mainpattern 301 and the auxiliary patterns 302. The auxiliary patterns 302are made from a second shielding portion.

In this embodiment, the first shielding portion 301A and the secondshielding portion working as the auxiliary patterns 302 are made fromone shielding film 307 of, for example, a metal film such as a Cr(chromium) film formed on the transparent substrate 300.

In other words, Embodiment 3 is different from Embodiment 1 in using amask enhancer composed of a shielding portion and a phase shifter andauxiliary patterns (diffraction light generation patterns) made from ashielding portion alone. In the photomask shown in FIGS. 20A and 20B, amask pattern consists of the main pattern 301 and the auxiliary patterns302. Also, an area on the transparent substrate 300 where the maskpattern is not formed corresponds to a transparent portion (opening).Furthermore, there is a relationship of the opposite phases betweenlight passing through the phase shifter 301B and light passing throughthe transparent portion (specifically, a relationship that a phasedifference between these lights is not less than (150+360×n) degrees andnot more than (210+360×n) degrees (wherein n is an integer).

According to Embodiment 3, since the main pattern 301 includes the phaseshifter 301B, light passing through the transparent portion can bepartially cancelled by light passing through the phase shifter 301B.Therefore, the contrast in a light intensity distribution of a shieldedimage corresponding to the main pattern 301 can be emphasized.Furthermore, since the auxiliary patterns 302 are provided separatelyfrom the main pattern 301, when the auxiliary patterns 302 are disposedin appropriate positions, diffraction light for interfering with thelight passing through the phase shifter 301B of the main pattern 301 canbe generated. Accordingly, the defocus characteristic of a transferredimage of the main pattern 301 can be improved, resulting in improvingthe DOF characteristic.

Also, according to Embodiment 3, since the phase shifter 301B isdisposed at the center of the first shielding portion 301A in the shapecorresponding to the outline of the main pattern 301, the contrast ofthe light intensity distribution at the center of the shielded imagecorresponding to the main pattern 301 can be emphasized. As a result,for example, a fine line pattern can be formed while keeping a gooddefocus characteristic.

Furthermore, according to Embodiment 3, since the phase shifter 301B isformed by trenching the transparent substrate 300, a good defocuscharacteristic can be exhibited in the pattern formation. Specifically,the phase shifter 301B is formed by forming an opening in the shieldingfilm 307 (shielding portion) and trenching the transparent substrate 300within the opening, and therefore, the phase shifter 301B can attain ahigh transmitting property. Also, since the intensity of light in theopposite phase passing through the inside of the main pattern 301 can becontrolled in accordance with the dimension of the opening formed in theshielding portion, the light in the opposite phase passing through themain pattern 301 can be easily optimized. Therefore, a very good defocuscharacteristic can be exhibited in the pattern formation. Specifically,the mask dimension (the dimension of the main pattern) can be controlledin accordance with the width of a part of the shielding portionsurrounding the phase shifter, and the intensity of the light in theopposite phase passing through the main pattern can be controlled inaccordance with the dimension of the opening formed in the shieldingportion. Therefore, as a peculiar effect of this photomask, the maskdimension and the intensity of the light in the opposite phase can beindependently controlled. Accordingly, similarly to Embodiment 1, whiledefinitely attaining effects resulting from the control of the light inthe opposite phase, such as the effect to improve the focuscharacteristic and the effect to improve the contrast of a fine pattern,a desired pattern dimension can be easily realized.

In Embodiment 3, a photomask that can attain the same effects as thoseof the photomask shown in FIG. 20B can be also realized as shown in, forexample, FIG. 21A, in which a shielding film 307 is removed from amultilayer structure of a transparent substrate 300 and the shieldingfilm 307 in a phase shifter formation region and a transparent portionformation region and the transparent substrate 300 is trenched in thetransparent portion formation region.

Alternatively, in Embodiment 3, the main pattern 301 including the phaseshifter 301B and the auxiliary patterns 302 may be formed by employing astructure as shown in, for example, FIG. 21B or 21C, in which ashielding film 307 is formed above a transparent substrate 300 with aphase shift film 308 made from a material with high transmittancesandwiched between the transparent substrate 300 and the shielding film307. Specifically, as shown in FIG. 21B, in a mask structure in whichthe phase shift film 308 with high transmittance is deposited on thetransparent substrate 300 and the shielding film 307 is deposited on thephase shift film 308, the shielding film 307 is removed in the phaseshifter formation region and the transparent portion formation regionand the phase shift film 308 is removed in the phase shifter formationregion. Also in this manner, a photomask that can attain the sameeffects as those of the photomask of FIG. 20B can be realized. Also, inthe photomask of FIG. 21B, the phase of the phase shifter 301B can behighly precisely controlled. On the other hand, as shown in FIG. 21C, ina multilayer mask structure similar to that of FIG. 21B, the shieldingfilm 307 is removed in the phase shifter formation region and thetransparent portion formation region and the phase shift film 308 isremoved in the transparent portion formation region. Also in thismanner, a photomask that can attain the same effects as those of thephotomask of FIG. 20B can be realized.

At this point, it will be described that a photomask easily inspectablecan be realized when the photomask is fabricated by forming a shieldingportion of a metal film on a transparent substrate and forming a phaseshifter by trenching the transparent substrate as in this embodiment.The transmittance of a material having a light transmitting property isvaried depending upon the wavelength of light. Therefore, in some cases,a mask inspection cannot be carried out without using light of the samewavelength as exposing light. Specifically, in the case where a materialwith low transmittance against exposing light is inspected by usinglight of a higher wavelength than the exposing light, for example, thematerial may have such high transmittance against the wavelength of thelight used in the inspection that the shielding property of a maskpattern cannot be inspected. However, as in this embodiment, when ametal film with a sufficient thickness that can substantially completelyshield light is used as a shielding portion, the metal film works as asubstantially complete shielding film against almost all lightsexcluding light of a wavelength in the X-ray region. Accordingly, evenwhen the wavelength of the exposing light is different from thewavelength of the light used in the inspection, a photomask like that ofthis embodiment can be easily inspected.

Modification of Embodiment 3

A photomask according to a modification of Embodiment 3 of the inventionwill now be described with reference to the accompanying drawing.

FIG. 22 is a plan view of a mask pattern of the photomask of thismodification. In FIG. 22, like reference numerals are used to refer tolike elements used in the photomask of Embodiment 3 shown in FIGS. 20Aand 20B so as to omit the description.

As a first characteristic of this modification, an auxiliary pattern 302(with a width D1) is disposed in a position away from the center of aphase shifter 301B of a main pattern 301 (with a width L) by a distanceλ/(2×sin φ).

As a second characteristic of this modification, a second auxiliarypattern 303 (with a width D2) is disposed in a position away from thecenter of the phase shifter 301B (with a width W) of the main pattern301 by a distance λ/(2×sin φ)+λ/(NA+sin φ), namely, in a position awayfrom the center of the auxiliary pattern 302 (hereinafter referred to asthe first auxiliary pattern) by a distance λ/(NA+sin φ) with atransparent portion sandwiched between the first auxiliary pattern 302and the second auxiliary pattern 303. The second auxiliary pattern 303is made from a similar shielding portion to that used for the firstauxiliary pattern 302.

According to this modification, the effect to improve the DOF derivedfrom the diffraction light attained by Embodiment 3 can be definitelyrealized.

It is noted, in this modification, that either of the first auxiliarypattern 302 and the second auxiliary pattern 303 may be omitted.

Furthermore, in this modification, even when the distance between thephase shifter 301B and the first auxiliary pattern 302 is approximate toλ/(2×sin φ), the above-described effect can be attained to some extent.

Also, in this modification, even when the distance between the phaseshifter 301B and the second auxiliary pattern 303 is approximate toλ/(2×sin φ)+λ/(NA+sin φ), the aforementioned effect can be attained tosome extent.

Herein, these approximate values of the distances of the first auxiliarypattern 302 and the second auxiliary pattern 303 for attaining theeffect to some extent correspond to the allowable ranges of thepositions of the diffraction light generation patterns described inModification 1 of Embodiment 1.

Furthermore, in this modification, with respect to the oblique incidentangle φ, sin( φ is preferably not less than 0.40×NA and not more than0.80×NA, and more preferably not less than 0.58×NA and not more than0.70×NA. In the case where the exposure is performed by using annularillumination, sin(p is preferably not less than 0.60×NA and not morethan 0.80×NA. In the case where the exposure is performed by usingquadrupole illumination, sin φ is preferably not less than 0.40×NA andnot more than 0.60××NA (see Modification 2 of Embodiment 1).

Moreover, in this modification, the width L of the main pattern 301 ispreferably larger than the width W of the phase shifter 301B by at least2×20 nm (in the actual dimension on the mask), and in particular, ispreferably not less than twice of a quarter of the exposure wavelength(the wavelength of the exposing light). Specifically, in the maskenhancer structure of the main pattern, the width of a part of theshielding portion sandwiched between the phase shifter and thetransparent portion is preferably at least 20 nm (in the actualdimension on the mask), and in particular, is preferably not less than aquarter of the exposure wavelength. However, since this photomaskemploys the mask enhancer structure, the width of the main pattern ispreferably 0.8×λ/NA or less, and therefore, the width of a part of theshielding portion sandwiched between the phase shifter and thetransparent portion preferably does not exceed 0.4×λ/NA (described indetail in Modification 3 of Embodiment 1).

Also, in this modification, the width D2 of the second auxiliary pattern303 is preferably larger than the width D1 of the first auxiliarypattern 302. In particular, the width D2 is preferably not less than 1.2times as large as the width D1 (described in detail in Modification 4 ofEmbodiment 1).

Embodiment 4

A photomask according to Embodiment 4 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 23A is a plan view of the photomask of Embodiment 4, and FIG. 23Bis a cross-sectional view thereof taken along line XXIII-XXIII of FIG.23A.

As shown in FIGS. 23A and 23B, a line-shaped main pattern 401 to betransferred through exposure is provided on a transparent substrate 400.The main pattern 401 is made from a phase shifter. The phase shifter isformed by, for example, trenching the transparent substrate 400. A pairof auxiliary patterns 402 that diffract exposing light and are nottransferred through the exposure are provided on the transparentsubstrate 400 on both sides of the main pattern 401 so as to sandwich atransparent portion between the main pattern 401 and the auxiliarypattern 402. The auxiliary pattern 402 is made from a semi-shieldingportion for partially transmitting the exposing light.

Specifically, Embodiment 4 is different from Embodiment 1 in employing,instead of the mask enhancer structure, a structure in which the mainpattern 401 is composed of the phase shifter alone. In the photomask ofFIGS. 23A and 23B, a mask pattern consists of the main pattern 401 andthe auxiliary patterns 402. Also, an area on the transparent substrate400 where the mask pattern is not formed corresponds to a transparentportion (opening).

Furthermore, there is a relationship of the opposite phases betweenlight passing through the phase shifter working as the main pattern 401and light passing through the transparent portion (specifically, arelationship that a phase difference between these lights is not lessthan (150+360×n) degrees and not more than (210+360×n) degrees (whereinn is an integer)).

Moreover, there is a relationship of the same phase between lightpassing through the semi-shielding portion working as the auxiliarypattern 402 and light passing through the transparent portion(specifically, a relationship that a phase difference between theselights is not less than (−30+360×n) degrees and not more than (30+360×n)degrees (wherein n is an integer)).

According to Embodiment 4, since the main pattern 401 is made from thephase shifter, the light passing through the transparent portion can bepartially cancelled by the light passing through the phase shifter.Therefore, the contrast in a light intensity distribution of a shieldedimage corresponding to the main pattern 401 can be emphasized. Also,since the auxiliary patterns 402 having low transmittance are providedseparately from the main pattern 401, diffraction light that interfereswith the light passing through the phase shifter working as the mainpattern 401 can be generated by disposing the auxiliary patterns 402 inappropriate positions. Accordingly, a defocus characteristic of atransferred image of the main pattern 401 can be improved, resulting inimproving the DOF characteristic.

Furthermore, according to Embodiment 4, since the auxiliary patterns 402are made from the semi-shielding portion, the degree of freedom in thearrangement of the auxiliary patterns can be increased. Therefore, theperiodicity in the arrangement of the patterns including the mainpattern 401 can be increased, so that the DOF characteristic can befurther improved. Also, since the auxiliary patterns 402 are made fromthe semi-shielding portion, these auxiliary patterns can be made thickunder restriction that they are not transferred through the exposure,and hence, the auxiliary patterns can be easily processed.

Moreover, according to Embodiment 4, since the phase shifter working asthe main pattern 401 is formed by trenching the transparent substrate400, a very good defocus characteristic can be exhibited in the patternformation.

In Embodiment 4, since the main pattern 401 is composed of the phaseshifter alone, it is impossible to attain the effect attained by themask enhancer structure used in Embodiments 1 through 3, namely, thepeculiar effect to easily realize a desired dimension in the patternformation while controlling both the contrast and the defocuscharacteristic by adjusting the dimension of a mask enhancer and thedimension of a phase shifter (opening) provided in the mask enhancer.However, when merely the defocus characteristic is desired to beimproved, a mask enhancer may be thus replaced with a simple phaseshifter.

Also in Embodiment 4, the transmittance of the auxiliary patterns 402 ispreferably not less than 6% and not more than 50%. Thus, the effect toimprove the DOF derived from the diffraction light can be definitelyrealized while preventing an unexposed portion from being formed in aresist due to a too high shielding property of the auxiliary pattern402.

In Embodiment 4, a mask cross-sectional structure shown in FIG. 23C maybe employed instead of the mask cross-sectional structure of FIG. 23B.Specifically, as shown in FIG. 23C, in a multilayer structure in which asemi-shielding film 406 and a phase shift film 408 made from a materialwith high transmittance are successively formed on a transparentsubstrate 400, the phase shift film 408 is removed in a region otherthan a phase shifter formation region (namely, a main pattern formationregion), and the semi-shielding film 406 is removed in a transparentportion formation region. When the structure shown in FIG. 23C isemployed, the transmittance of the phase shifter working as the mainpattern 401 can be easily made lower than the transmittance of thesemi-shielding portion working as the auxiliary patterns 402. In thiscase, when the transmittance of the phase shifter is set to 15% or less,not only a fine pattern but also a whole main pattern in an arbitrarydimension can be constructed by using a phase shifter. Therefore, aphotomask in which patterns in arbitrary dimensions are mixedly formedas a main pattern can be easily fabricated.

Modification of Embodiment 4

A photomask according to a modification of Embodiment 4 of the inventionwill now be described with reference to the accompanying drawings.

FIG. 24 is a plan view of a mask pattern of the photomask of themodification of Embodiment 4. In FIG. 24, like reference numerals areused to refer to like elements used in the photomask of Embodiment 4shown in FIGS. 23A and 23B so as to omit the description.

As a first characteristic of this modification, an auxiliary pattern 402(with a width D1) is disposed in a position away from the center of amain pattern 401 (with a width W) namely, the center of a phase shifter,by a distance λ/(2×sin φ).

As a second characteristic of this modification, a second auxiliarypattern 403 (with a width D2) that diffracts exposing light and is nottransferred through exposure is disposed in a position away from thecenter of the phase shifter working as the main pattern 401 by adistance λ/(2×sin φ)+λ(NA+sin φ), namely, in a position away from thecenter of the auxiliary pattern 402 (hereinafter referred to as thefirst auxiliary pattern) by a distance λ/(NA+sin φ), with a transparentportion sandwiched between the first auxiliary pattern 402 and thesecond auxiliary pattern 403. The second auxiliary pattern 403 is madefrom a similar shielding portion to that used for the first auxiliarypattern 402.

According to this modification, the effect to improve the DOF derivedfrom the diffraction light attained by Embodiment 4 can be definitelyrealized.

It is noted, in this modification, that either of the first auxiliarypattern 402 and the second auxiliary pattern 403 may be omitted.

Furthermore, in this modification, even when the distance between thephase shifter working as the main pattern 401 and the first auxiliarypattern 402 is approximate to λ/(2×sin φ), the above-described effectcan be attained to some extent.

Also, in this modification, even when the distance between the phaseshifter working as the main pattern 401 and the second auxiliary pattern403 is approximate to λ/(2×sin φ)+λ/(NA+sin φ), the aforementionedeffect can be attained to some extent.

Herein, these approximate values of the distances of the first auxiliarypattern 402 and the second auxiliary pattern 403 for attaining theeffect to some extent correspond to the allowable ranges of thepositions of the diffraction light generation patterns described inModification 1 of Embodiment 1.

Furthermore, in this modification, with respect to the oblique incidentangle φ, sin φ is preferably not less than 0.40×NA and not more than0.80×NA, and more preferably not less than 0.58×NA and not more than0.70×NA. In the case where the exposure is performed by using annularillumination, sin φ is preferably not less than 0.60×NA and not morethan 0.80×NA. In the case where the exposure is performed by usingquadrupole illumination, sin φ is preferably not less than 0.40×NA andnot more than 0.60 ×NA (see Modification 2 of Embodiment 1).

Also, in this modification, the width D2 of the second auxiliary pattern403 is preferably larger than the width D1 of the first auxiliarypattern 402. In particular, the width D2 is preferably not less than 1.2times as large as the width D1 (described in detail in Modification 4 ofEmbodiment 1).

Furthermore, although the semi-shielding portion is used for forming theauxiliary patterns 402 and 403 in this modification, a shielding portionmay be used instead. In this case, as compared with the case where thesemi-shielding portion is used for forming the auxiliary patterns, thecontrast between the main pattern and the auxiliary patterns is lowered,but needless to say, a photomask that can realize a large DOF can beobtained by disposing the auxiliary patterns in the positions describedin this modification.

Moreover, in the case where a simplified mask structure described belowis used instead of the mask structure of this modification, although theeffects to improve the contrast and the DOF in the pattern formation arereduced as compared with those attained by this modification, theseeffects can be improved as compared with those attained by theconventional technique.

Specifically, when auxiliary patterns 412 and 413 made from a shieldingportion as shown in FIG. 25A are used instead of the auxiliary patterns402 and 403 made from the semi-shielding portion of this modification(see FIG. 24), the degree of freedom in the arrangement of the auxiliarypatterns is lowered because the shielding property of the auxiliarypatterns is increased. However, also in the mask structure shown in FIG.25A, since the main pattern 401 is made from a phase shifter, the effectto improve the DOF can be attained by disposing the auxiliary patterns412 and 413 in the positions similar to those of the auxiliary patterns402 and 403 of this modification. Also, since the semi-shielding portionis replaced with the shielding portion, although the performance in thepattern formation is lowered, a mask inspection can be definitelycarried out (see Embodiment 3 ).

FIGS. 25B and 25C are cross-sectional views for showing variations ofthe cross-sectional structure taken along line XXV-XXV of FIG. 25A.

In the structure of FIG. 25B, a phase shifter working as a main pattern401 is formed by trenching a transparent substrate 400. Also, eachauxiliary pattern (with the second auxiliary pattern 413 omitted in thedrawing) is made from a shielding film 407 formed on the transparentsubstrate 400. In the structure of FIG. 25B, the phase shifter canattain sufficiently high transmittance, so that the effect to improvethe DOF can be sufficiently attained.

In the structure of FIG. 25C, in a multilayer structure in which a phaseshift film 408 and a shielding film 407 are successively formed on atransparent substrate 400, the shielding film 407 is removed in a regionother than an auxiliary pattern formation region and the phase shiftfilm 408 is removed in a transparent portion formation region.Specifically, the main pattern 401 is composed of a single-layerstructure of the phase shift film 408, and each auxiliary pattern 412 or413 (with the second auxiliary pattern 413 omitted in the drawing) iscomposed of a multilayer structure including the phase shift film 408and the shielding film 407. In the structure of FIG. 25C, when thetransmittance of the phase shifter is set to 15% or less, not only afine pattern but also a large pattern can be constructed by using aphase shifter. Therefore, a photomask in which patterns in arbitrarydimensions ranging from a fine pattern to a large pattern are mixedlydisposed as a main pattern can be easily fabricated.

In the case where auxiliary patterns 422 and 423 each made from a phaseshifter as shown in FIG. 26 are used instead of the auxiliary patterns402 and 403 made from the semi-shielding portion of this modification(see FIG. 24), although the effect to make the shielding property of theauxiliary patterns lower than that of the main pattern is reduced, theeffect to improve the DOF can be sufficiently attained. The structureshown in FIG. 26 can be realized merely by patterning a phase shift filmformed on a transparent substrate, and therefore, the photomaskprocessing can be eased.

Alternatively, a main pattern 411 made from a shielding portion andauxiliary patterns 412 and 413 made from a shielding portion as shown inFIG. 27 may be used instead of the main pattern 401 made from the phaseshifter and the auxiliary patterns 402 and 403 made from thesemi-shielding portion of this modification (see FIG. 24). In this case,although the effect to emphasize the shielding property and the effectto improve the DOF owing to the main pattern 411 are reduced as comparedwith those attained in this modification, the effect to improve the DOFcan be attained to some extent. Since the mask pattern is made from theshielding portion alone in the mask structure of FIG. 27, the photomaskprocessing, the inspection and the like can be much eased.

Embodiment 5

A pattern formation method according to Embodiment 5 of the invention,and more specifically, a pattern formation method using a photomaskaccording to any of Embodiments 1 through 4 (hereinafter referred to asthe present photomask), will be described with reference to theaccompanying drawings.

FIGS. 28A through 28D are cross-sectional views for showing proceduresin the pattern formation method of Embodiment 5.

First, as shown in FIG. 28A, a target film 501 of, for example, a metalfilm or an insulating film is formed on a substrate 500. Thereafter, asshown in FIG. 28B, a positive resist film 502 is formed on the targetfilm 501.

Next, as shown in FIG. 28C, the present photomask, such as the photomaskaccording to Embodiment 1 shown in FIG. 1B, is irradiated with exposinglight 503, so as to expose the resist film 502 to transmitted light 504having passed through the photomask.

On a transparent substrate 100 of the photomask used in the procedureshown in FIG. 28C, a line-shaped main pattern 101 to be transferredthrough the exposure is provided. The main pattern 101 is composed of afirst semi-shielding portion 101A having first transmittance forpartially transmitting the exposing light and a phase shifter 101B. Thefirst semi-shielding portion 101A is formed so as to surround the phaseshifter 101B in a line shape. The phase shifter 101B is formed by, forexample, trenching the transparent substrate 100. A pair of auxiliarypatterns 102 that diffract the exposing light and are not transferredthrough the exposure are provided on the transparent substrate 100 onthe both sides of the main pattern 101 so as to sandwich a transparentportion between the main pattern 101 and the auxiliary pattern 102. Theauxiliary pattern 102 is made from a second semi-shielding portionhaving second transmittance for partially transmitting the exposinglight.

In the exposure performed in FIG. 28C, the resist film 502 is subjectedto the exposure by using an oblique incident exposure light source. Inthis case, since the semi- shielding portion having low transmittance isused in the mask pattern, the entire resist film 502 is exposed at weakenergy. However, as shown in FIG. 28C, it is only a latent image portion502 a of the resist film 502 corresponding to a region other than themain pattern 101 that is irradiated at exposing energy sufficiently highfor allowing the resist to dissolve in development.

Next, as shown in FIG. 28D, the resist film 502 is developed so as toremove the latent image portion 502 a. Thus, a resist pattern 505corresponding to the main pattern 101 is formed.

According to Embodiment 5, since the pattern formation method is carriedout by using the present photomask (specifically, the photomaskaccording to Embodiment 1), the same effects as those described inEmbodiment 1 can be attained. Specifically, the substrate (wafer) onwhich the resist is applied is subjected to the oblique incidentexposure through the present photomask. At this point, since the maskenhancer (the main pattern 101) having the phase shifter (the opening)has a very strong shielding property, merely a portion of the resistcorresponding to a region other than the mask enhancer can be irradiatedat the exposing energy sufficiently high for allowing the resist todissolve in the development. Also, since the latent image formed byusing the mask enhancer has very high contrast and a good defocuscharacteristic, a fine pattern with a large DOF can be formed.

Although the photomask according to Embodiment 1 is used in Embodiment5, in the case where a photomask according to any of Embodiments 2through 4 is used instead, the same effects as those described in thecorresponding embodiment can be attained.

Although the positive resist process is employed in Embodiment 5, thesame effects can be attained by employing the negative resist processinstead.

In Embodiment 5, oblique incident illumination (oblique incidentexposure) is preferably used in the procedure shown in FIG. 28C forirradiating the resist film with the exposing light 503. Thus, in alight intensity distribution of the light having passed through thepresent photomask, contrast between a region corresponding to the mainpattern and a region corresponding to the transparent portion can beimproved. Also, the focus characteristic of the light intensitydistribution can be improved. Accordingly, the exposure margin and thefocus margin are improved in the pattern formation. In other words, afine pattern can be formed with a good defocus characteristic.

Next, a method for calculating the oblique incident angle that plays asignificant role in the oblique incident exposure using the presentphotomask having the auxiliary patterns (the diffraction lightgeneration patterns) will be described.

In the case where a point light source is used as the gracing incidenceexposure light source, the oblique incident angle is definitely defined(see FIG. 5). In the case where a general light source with an area isused, however, there are a plurality of oblique incident angles.

FIGS. 29A through 29E are diagrams for showing principle calculationmethods for the oblique incident angle that are defined by the presentinventor for calculating the optimum position of a diffraction lightgeneration pattern also in using a light source with an area.

FIG. 29A shows a calculation method for the oblique incident angle inusing annular illumination. As shown in FIG. 29A, in the annularillumination, the inner diameter S1 of the annular light sourcecorresponds to a minimum oblique incident angle φ1, and the outerdiameter S2 of the annular light source corresponds to a maximum obliqueincident angle φ2. Accordingly, the oblique incident angle φ used forcalculating the position of a diffraction light generation pattern isdefined on the basis of a light source emitting light from a position S(=(S1+S2)/2) calculated by using the inner diameter S1 and the outerdiameter S2. Specifically, the oblique incident angle φ is obtained as(φ1+φ2)/2. Also, when the diameters S1 and S2 have values standardizedby the numerical aperture NA, the oblique incident angle φ in thephotomask according to any of Embodiments 1 through 4 can be set on thebasis of sin φ=S×NA=(S1+S2)×NA/2. However, in the pattern formationmethod using the annular illumination, lighting and a photomask arepreferably adjusted so that the oblique incident position S can be notless than0.6 and not more than 0.8, and more preferably adjusted so thatthe oblique incident position S can be approximate to 0.7 (seeModification 2 of Embodiment 1).

It goes without saying that the oblique incident angle φ can be set toan arbitrary value not smaller than φ1 and not larger than φ2. In otherwords, it goes without saying that the oblique incident angle φ can beset to an arbitrary value satisfying a relationship, S1×NA≦sin φ≦S2×NA.

As described in Embodiment 1, in the case where the oblique incidentangle φ satisfies sin φ<NA/3 in the oblique incident exposure, theeffect to improve the defocus characteristic cannot be attained.Therefore, also in using a light source with an area, the obliqueincident angles φ preferably includes merely values for attaining asufficient effect to improve the defocus characteristic. Also, when alight source used in the exposure emits light having an oblique incidentangle φ satisfying sin φ<NA/3, the exposure is preferably performed byusing a mask in which the diffraction light generation pattern isoptimally provided by ignoring this light entering at the unpreferableangle. Thus, as compared with the case where the diffraction lightgeneration pattern is provided in consideration of the light entering atthe unpreferable angle, a better defocus characteristic can be exhibitedin the pattern formation. Accordingly, the minimum angle ξ of theoblique incident angle φ is a value defined as sin ξ=0.4×NA.Specifically, the oblique incident angle φ used in calculating theposition of a diffraction light generation pattern is (ξ+φ2)/2. In otherwords, the oblique incident angle φ is defined as sin φ=(0.4+S2)×NA/2.

FIGS. 29B through 29E respectively show the calculation methods for theoblique incident angle in using the quadrupole lighting. In using thequadrupole lighting, as shown in each of these drawings, the obliqueincident angle is calculated by using the XY coordinate system havingthe center of the quadrupole light source (four-eyed light source)(hereinafter referred to as the light source center) as the origin.Specifically, in using the quadrupole lighting, the oblique incidentangle is optimized with respect to each pattern parallel to the X axisor the Y axis of the XY coordinate system. In other words, the obliqueincident angle is not defined on the basis of the distance from thelight source center to each light source but is defined by using acoordinate value of each light source on the X axis or the Y axis. Now,the optimization of the oblique incident angle with respect to a patternparallel to the Y axis will be described, and the following descriptionis similarly applicable to the optimization of the oblique incidentangle with respect to a pattern parallel to the X axis. First, theminimum oblique incident angle is defined by a value that is the closestto the origin among absolute values of the X coordinate values of therespective light sources of the quadrupole light source. Specifically,the minimum oblique incident angle is defined by a value x1 shown ineach of FIGS. 29B through 29E. Similarly, the maximum oblique incidentangle is defined by a value that is farthest from the origin among theabsolute values of the X coordinate values of the respective lightsources of the quadrupole light source, namely, a value x2 shown in eachof FIGS. 29B through 29E. Accordingly, in using the quadrupole lighting,the oblique incident angle φ used for calculating the position of adiffraction light generation pattern is set in accordance with sinφ=S×NA=(x1+x2)×NA/2. However, in the pattern formation using thequadrupole lighting, lighting and a photomask are preferably adjusted sothat the oblique incident position S can be not less than 0.4 and notmore than 0.6, and more preferably adjusted so that the oblique incidentposition S can be approximate to 0.5 (see Modification 2 of Embodiment1).

It goes without saying that the oblique incident angle φ can be set toan arbitrary value satisfying a relationship, x1×NA≦sin φ≦x2×NA.

Also in using the quadrupole lighting shown in any of FIGS. 29B through29E, similarly to the annular illumination shown in FIG. 29A, theminimum angle ξ of the oblique incident angle φ preferably has a valuedefined as sin ξ=0.4×NA. Specifically, the oblique incident angle φ usedin calculating the position of a diffraction light generation pattern isdefined as sin φ=(0.4+x2)×NA/2.

Embodiment 6

A mask data creation method according to Embodiment 6 of the invention,more specifically, a mask data creation method for a photomask accordingto any of Embodiments 1 through 4 (hereinafter referred to as thepresent photomask) using the center line enhancement method, the outlineenhancement method and a diffraction light generation pattern, will bedescribed with reference to the accompanying drawings. In thisembodiment, the functions, the properties and the like of the respectiveelements of the photomask are the same as those of the correspondingelements of the present photomask described above unless otherwisementioned.

Before describing specific processing, a significant point of the maskdata creation method for the present photomask will be explained. In thepresent photomask, formation of even one isolated pattern is concernedwith a phase shifter, a shielding or semi-shielding portion surroundingthe phase shifter and a diffraction light generation pattern (anauxiliary pattern) disposed around them. Therefore, in order to set apattern dimension employed in the pattern formation, namely, a CD(critical dimension), to a desired value, it is necessary to determine aplurality of element values such as the width of the phase shifter, thewidth of the shielding or semi-shielding portion and the position andthe width of the diffraction light generation pattern. Also,occasionally, the number of combinations of these element values forrealizing a desired CD is not one but plural. Therefore, in the maskdata creation method of this embodiment, values of significant elementsfor attaining a maximum margin in the pattern formation are priorlydetermined, and values of elements less affecting the margin in thepattern formation are subsequently controlled to adjust the patterndimension.

Specifically, as elements largely affecting the margin in the patternformation, preferably, the position and the width of the phase shifterare first determined, the position and the width of the auxiliarypattern are determined secondly, and the width of a part of theshielding or semi-shielding portion surrounding the phase shifter,namely, the width of a part sandwiched between the phase shifter and atransparent portion, is ultimately controlled, so as to create mask datafor realizing a desired CD. Now, the specific processing will bedescribed.

FIG. 30 is a flowchart of the mask data creation method of Embodiment 6,more specifically, a method for forming a mask pattern for an LSIworking as a shielding pattern on a mask on the basis of a desired finepattern. FIGS. 31A through 31G are diagrams for showing exemplifiedspecific mask patterns formed in respective procedures in the mask datacreation method of Embodiment 6.

FIG. 31A shows a desired pattern to be formed by using a mask pattern.

Specifically, the pattern 600 shown in FIG. 31A corresponds to a regionwhere a resist is not desired to be sensitized in exposure using thepresent photomask. In the description of the pattern formation in thisembodiment, the positive resist process is employed unless otherwisementioned. In other words, the description is given under assumptionthat an exposed portion of a resist is removed and an unexposed portionof the resist remains as a resist pattern. Accordingly, in the casewhere the negative resist process is employed, the description can besimilarly applied by assuming that an exposed portion of a resistremains as a resist pattern and an unexposed portion is removed.

First, in step S1, the desired pattern 600 shown in FIG. 31A is input toa computer used for the mask data creation.

Next, in step S2, the desired pattern of FIG. 31A is resized byenlarging or reducing it depending upon whether over-exposure orunder-exposure is employed in the exposure of a photomask to be createdin this embodiment. Alternatively, the desired pattern may be resized inorder to intentionally adjust the dimension in accordance withdimensional change caused in various procedures during the patternformation. The resized pattern is defined as a main pattern 601 madefrom a semi-shielding portion as shown in FIG. 31B.

Then, in step S3, as shown in FIG. 31C, the shape (such as the width;which also applies in the following description) of a phase shifter 602to be disposed at the center of a part of the main pattern 601 with apredetermined or smaller dimension is determined. At this point, thephase shifter 602 should be completely contained within the main pattern601, namely, the semi-shielding pattern. In other words, the outermostedge of the main pattern 601 corresponds to the edge of thesemi-shielding pattern.

The width of the phase shifter to be determined at this point ispreferably adjusted as follows: Specifically, the width of the phaseshifter is previously adjusted at this point so that the width of a partof the semi-shielding portion surrounding the phase shifter sandwichedbetween the phase shifter and a transparent portion can be preventedfrom being smaller than a predetermined width after being changed for CDadjustment subsequently performed. This predetermined width ispreferably not less than 20 nm in the actual dimension on the mask ornot less than ¼ of the exposure wavelength. Therefore, the width of thephase shifter is determined so that a dimension larger than thepredetermined width can be secured, at this point, as the width of thepart sandwiched between the phase shifter and the transparent portionand that a CD predicted under this condition cannot be larger than adesired value. Specifically, with the width of the phase shifter forrealizing the desired CD under the aforementioned condition defined asthe maximum phase shifter width, the phase shifter is disposed to have awidth smaller than the maximum phase shifter width for optimizing thecontrast and the DOF of the patterns. Thus, there is no need to adjustthe pattern dimension by changing the width of the phase shifterafterward. It is noted that the description has been given so far underassumption that the main pattern has the mask enhancer structure, andthe aforementioned processing may be omitted in creating mask data inwhich the main pattern is made from a phase shifter alone.

Next, in step S4, as shown in FIG. 31D, the shape of a phase shifter 602to be disposed in a peripheral portion of a part of the main pattern 601with a dimension larger than the predetermined dimension is determined.At this point, the phase shifter 602 should be completely containedwithin the main pattern 601, namely, the semi-shielding pattern, so thatthe outermost edge of the main pattern 601 can correspond to the edge ofthe semi-shielding pattern.

Then, in step S5, as shown in FIG. 31E, first-order diffraction lightgeneration patterns 603 and second-order diffraction light generationpatterns 604 made from a semi-shielding portion are disposed, asauxiliary patterns for diffracting the exposing light, in positions awayfrom the phase shifters 602 disposed in step S3 and step S4 respectivelyby predetermined distances (that are determined on the basis of theoblique incident angle and the like of illumination of a light sourceused in the exposure). For example, in the case where the phase shifter602 is in a line shape, a line-shaped diffraction light generationpattern is disposed in a position away from the phase shifter 602 by apredetermined distance to be parallel to the phase shifter 602. In thecase where there is another pattern in a position where the diffractionlight generation pattern is to be disposed, the diffraction lightgeneration pattern is not disposed in such a region where anotherpattern is present.

Through the aforementioned processing, the position and the width of thephase shifter and the position and the width of the diffraction lightgeneration pattern, which largely affect the margin in the patternformation, have been determined to have optimum values.

Next, in step S6, preparation is made for processing for adjusting thedimension of the mask pattern for forming a pattern with a desireddimension correspondingly to the mask pattern through the exposure usingthe present photomask. Specifically, preparation is made for processinggenerally designated as OPC (optical proximity correction). In thisembodiment, a mask pattern region that is to be adjusted in thedimension on the basis of prediction of the dimension in the patternformation, namely, the predicted CD, is limited to the edge of the mainpattern 601, namely, the edge of the semi-shielding pattern.Specifically, as shown in FIG. 31F, the outermost edge of the mainpattern 601 is set as a CD adjustment edge 605. In other words, the CD,that is, the dimension of the pattern to be formed, is adjusted by usingthe outermost edge of the semi-shielding portion used for forming themain pattern. Thus, with respect to the main pattern in which the phaseshifter is provided, the CD can be adjusted in accordance with the widthof the part of the semi-shielding portion sandwiched between the phaseshifter and the transparent portion. Accordingly, without changing theshapes of the phase shifters 602 and the diffraction light generationpatterns 603 and 604 disposed in the optimum positions against the phaseshifters 602, a mask pattern for realizing a desired CD can be formed.

Next, in step S7, the transmittances of the semi-shielding portion andthe phase shifter used in the mask pattern are set.

Then, in step S8, step S9 and step S10, the OPC processing (for example,model base OPC processing) is performed. Specifically, in step S8, adimension of a resist pattern formed by using the main pattern 601including the phase shifters 602 and the diffraction light generationpatterns 603 and 604 is predicted through simulation in consideration ofthe optical principle and a resist development characteristic. At thispoint, in the simulation, not only lithography processing but also otherprocessing accompanied with the pattern formation such as dry etchingmay be considered. Subsequently, in step S9, it is determined whether ornot the predicted dimension of the resist pattern accords with thedesired dimension. When the predicted dimension does not accord with thedesired dimension, in step S10, the CD adjustment edge 605 is moved onthe basis of a difference between the predicted dimension and thedesired dimension, so as to change the shape of the main pattern 601.

As a characteristic of this embodiment, the CD adjustment edge 605 setin step S6 alone is changed for realizing a mask pattern capable offorming a resist pattern with a desired dimension. Specifically, byrepeating the procedures of steps S8 through S10 until the predicteddimension of the resist pattern accords with the desired pattern, a maskpattern capable of forming a resist pattern with the desired dimensionis ultimately output in step S11. FIG. 31G shows an example of the maskpattern output instep S11.

Originally, it is a very large number of parameters of the presentphotomask, such as the width of the phase shifter, the width of the maskpattern (main pattern) and the position and the width of the auxiliarypattern, that affect the dimension of a pattern (resist pattern).

In contrast, in Embodiment 6, the significant parameters, that is, thewidths of the phase shifters 602 and the positions of the diffractionlight generation patterns 603 and 604, are first determined in order torealize a mask good at the significant pattern formation characteristicsuch as the contrast and the defocus characteristic. Thereafter, thepattern dimension is controlled by moving merely the outermost edge ofthe main pattern 601 that is set as the CD adjustment edge 605. Thus, amask pattern with good pattern formation characteristics can berealized.

Accordingly, when a photomask is formed on the basis of the mask datacreated by the method of this embodiment and the oblique incidentexposure is performed by using the photomask, high contrast and a verygood DOF characteristic can be attained in forming a fine pattern or afine space.

Also, according to Embodiment 6, since the phase shifter 602 is disposedat the center of the part of the main pattern 601 with the predeterminedor smaller dimension, a mask pattern capable of forming a finer desiredpattern and having good pattern formation characteristics can berealized.

Furthermore, according to Embodiment 6, the phase shifter 602 isdisposed in the peripheral portion of the main pattern 601, a maskpattern capable of forming a desired pattern in an arbitrary shape andhaving good pattern formation characteristics can be realized.

The mask data creation method has been described so far under assumptionthat a diffraction light generation pattern can be disposed in aposition for generating optimum diffraction light. Next, a mask datacreation method (particularly, the processing in step S5) employed inthe case where another main pattern is disposed in the vicinity of amain pattern will be described in detail. In the following description,an example of the mask pattern to be formed shown in FIG. 32 is usedinstead of the example of the mask pattern to be formed shown in FIG.31G. In FIG. 32, a reference numeral 701 denotes a main pattern to benoticed, reference numerals 702, 703, 704 and 705 denote other mainpatterns disposed in the vicinity of the main pattern 701. In thefollowing description, it is assumed that the optimum position of thecenter of a first-order diffraction light generation pattern is aposition away from the center of the phase shifter by a distance G0 andthe allowable range in the position of the center of the first-orderdiffraction light generation pattern is from a distance G1 to a distanceG2 (wherein G1<G0<G2). In this case, the distances G1 and G2 preferablyaccord with the allowable range in the position of the first-orderdiffraction light generation pattern described in detail inEmbodiment 1. Also, the optimum position of the center of a second-orderdiffraction light generation pattern is a position away from the centerof the phase shifter by a distance HO and the allowable range in theposition of the center of the second-order diffraction light generationpattern is from a distance H1 to a distance H2 (wherein H1<H0<H2). Inthis case, also the distances H1 and H2 preferably accord with theallowable range in the position of the second-order diffraction lightgeneration pattern described in detail in Embodiment 1.

Now, a method for forming diffraction light generation patterns inconsideration of the relationship between the main pattern 701 to benoticed and the other main patterns 702 through 705 formed in thevicinity will be described in detail. Each of the main patterns 701through 705 has the mask enhancer structure. Specifically, the mainpattern 701 is composed of a phase shifter 701B and a semi-shieldingportion 701A surrounding it, the main pattern 702 is composed of a phaseshifter 702B and a semi-shielding portion 702A surrounding it, the mainpattern 703 is composed of a phase shifter 703B and a semi-shieldingportion 703A surrounding it, the main pattern 704 is composed of a phaseshifter 704B and a semi-shielding portion 704A surrounding it, and themain pattern 705 is composed of a phase shifter 705B and asemi-shielding portion 705A surrounding it.

As shown in FIG. 32, it is assumed that the main pattern 701 is close tothe main pattern 702 in such a manner that a distance p1 between thecenters thereof satisfies p1<2×G1. In this case, no diffraction lightgeneration pattern is disposed between the main pattern 701 and the mainpattern 702.

Also, it is assumed that the main pattern 701 is close to the mainpattern 703 in such a manner that a distance p2 between the centersthereof satisfies 2×G1≦p2<2×G2. In this case, a first-order diffractionlight generation pattern 801 is disposed at the center between the mainpattern 701 and the main pattern 703.

Furthermore, it is assumed that the main pattern 701 is close to themain pattern 704 in such a manner that a distance p3 between the centersthereof satisfies 2×G2≦p3<2×H1. In this case, between the main pattern701 and the main pattern 704, a first-order diffraction light generationpattern 802 is disposed so as to have its center in a position away fromthe center of the main pattern 701 by the distance G0, and a first-orderdiffraction light generation pattern 803 is disposed so as to have itscenter in a position way from the center of the main pattern 704 by thedistance G0.

Moreover, it is assumed that the main pattern 701 is close to the mainpattern 705 in such a manner that a distance p4 between the centersthereof satisfies 2×H1≦p4<2×H2. In this case, between the main pattern701 and the main pattern 705, a first-order diffraction light generationpattern 804 is disposed so as to have its center in a position away fromthe center of the main pattern 701 by the distance G0, a second-orderdiffraction light generation pattern 805 is disposed at the centerbetween the main pattern 701 and the main pattern 705, and a first-orderdiffraction light generation pattern 806 is disposed so as to have itscenter in a position away from the center of the main pattern 705 by thedistance G0.

In the case where the center of the main pattern to be noticed is awayfrom the center of another adjacent main pattern by a distance 2×H2, apair of first-order diffraction light generation patterns are disposedbetween these main patterns so as to have their centers away from therespective centers of the main patterns by the distance G0, and a pairof second-order diffraction light generation patterns are disposedbetween these main patterns so as to have their centers away from therespective centers of the main patterns by the distance H0.

When the aforementioned method for forming diffraction light generationpatterns is employed, even if a main pattern is close to another mainpattern by an arbitrary distance, a preferred diffraction lightgeneration pattern can be definitely formed.

Although the description is given with respect to the mask patternhaving the mask enhancer structure using a semi-shielding portion inEmbodiment 6, the method of this embodiment is also applicable to a maskpattern having the mask enhancer structure using a shielding portion.Specifically, all elements made from the semi-shielding portions in thisembodiment can be replaced with shielding portions. Also, in this case,the procedure performed in step S4 for providing the phase shifter 602in the peripheral portion of the main pattern 601 may be omitted. In thecase where a shielding portion is used instead of the semi-shieldingportion, in forming a pattern with a dimension smaller than apredetermined dimension by using a mask pattern created by the method ofthis embodiment, an effect to largely improve the contrast or the DOFcan be attained. Specifically, in forming a fine space, the effect toimprove the contrast or the DOF is small. However, for example, informing a pattern of a gate layer of an LSI circuit desired to attain ahigh operation speed, namely, in forming a pattern in which thedimension of a transistor pattern alone is very small but no fine spacepattern is included, the aforementioned effect can be very remarkablyexhibited.

In creation of mask pattern data for a general LSI, it is significant toincrease the margin in forming a transistor pattern. Therefore, in thecase where main patterns are disposed in the vicinity of each other andhence diffraction light generation patterns for these main patternscannot be disposed in optimum positions, a diffraction light generationpattern is provided in an optimum position with respect to a mainpattern corresponding to a transistor region while a diffraction lightgeneration pattern for a main pattern corresponding to an interconnectregion is provided regardless of its optimum position. Now, this will bedescribed with reference to a flowchart shown in FIG. 33. The improvedflowchart of FIG. 33 is different from the flowchart of FIG. 30 inperforming the processing for providing diffraction light generationpatterns on the basis of the position of a phase shifter of a mainpattern in separate two steps. In other words, the procedure performedin step S5 of the flowchart of FIG. 30 is performed dividedly in twosteps, namely, steps S51 and S52 in the flowchart of FIG. 33.Specifically, first in step S51, an optimum diffraction light generationpattern is generated and arranged with respect to a phase shifter of amain pattern corresponding to a transistor region. Next, in step S52, adiffraction light generation pattern is generated with respect to aphase shifter of a main pattern disposed in a region other than thetransistor region. In this method, even when the main patterncorresponding to the transistor region is too close to another mainpattern corresponding to another region (such as an interconnect region)to simultaneously provide diffraction light generation patterns to bothof these main patterns, an optimum diffraction light generation patterncan be provided to the main pattern corresponding to the transistorregion. It is noted that the main pattern corresponding to a transistorregion can be easily extracted, for example, through processing forextracting overlap between a gate layer and an active layer on the basisof LSI design data.

FIG. 34 shows an example of the mask pattern to be created specificallyas a result of the processing performed in accordance with the flowchartof FIG. 33. As shown in FIG. 34, main patterns 710 through 712 arerespectively composed of phase shifters 710B through 712B and shieldingportions 710A through 712A. Also, first-order diffraction lightgeneration patterns 811 through 815 are arranged with respect to thesemain patterns 710 through 712. In this case, the phase shifter 710B is aphase shifter disposed in a transistor region, and the other phaseshifters 711B and 712B are phase shifters disposed in a region otherthan the transistor region. Also, it is assumed that the position of anoptimum first-order diffraction light generation pattern with respect toa phase shifter is a position away from the center of the phase shifterby a distance G0 and the allowable range in the position of thefirst-order diffraction light generation pattern is from a distance G1through a distance G2. Furthermore, it is assumed that the main pattern710 is close to the main pattern 711 that is close to the main pattern712 and the distance between the centers of the adjacent main patternsis a distance p, wherein the distance p has a value not less than 2×G1and smaller than 2×G2. Moreover, each of the diffraction lightgeneration patterns 812 and 815 is disposed in a region sandwichedbetween the adjacent close main patterns. The other diffraction lightgeneration patterns 811, 813 and 814 are disposed with respect to themain patterns not close to another main pattern. As shown in FIG. 34,the diffraction light generation pattern 815 disposed between the mainpatterns 711 and 712 provided in the region other than the transistorregion is disposed at the center of these main patterns. On the otherhand, the diffraction light generation pattern 812 disposed between themain pattern 710 provided in the transistor region and the main pattern711 is disposed to have its center in a position away from the center ofthe phase shifter 710B of the main pattern 710 by the distance G0. Inother words, the phase shifter disposed in the transistor region ispriorly provided with the diffraction light generation pattern arrangedin the optimum position.

In the improved flowchart of FIG. 33, a diffraction light generationpattern is provided in an optimum position priorly with respect to amain pattern disposed in a transistor region by performing the procedureof step S5 of the flowchart of FIG. 30 in the two steps. However,needless to say, diffraction light generation patterns may besimultaneously provided in a transistor region and in another region inone step. Furthermore, although a transistor region is assumed to be asignificant region in the pattern formation, when a region other thanthe transistor region is significant in the pattern formation, thetransistor region is replaced with the other significant region in theaforementioned improved flowchart.

Furthermore, in Embodiment 6, the mask data creation method for aphotomask in which a main pattern has the mask enhancer structure hasbeen mainly described. However, through the aforementioned procedures,mask data for a photomask in which a main pattern does not have the maskenhancer structure can be created. Specifically, in the case where amain pattern is made from a phase shifter alone, the edge of the phaseshifter corresponds to the edge of the main pattern, and hence, the CDadjustment can be performed in accordance with the width of the phaseshifter. Alternatively, in the case where a main pattern is made from ashielding pattern alone, the edge of the shielding pattern correspondsto the edge of the main pattern, and hence, the CD adjustment can beperformed in accordance with the width of the shielding pattern. In thiscase, one of or both of the procedures in steps S3 and S4 of theflowchart of FIG. 30 may be omitted.

Moreover, in each of Embodiments 1 through 6, the description is givenwith respect to a transmission photomask, which does not limit theinvention. The present invention is applicable to a reflection mask byreplacing the transmission phenomenon of exposing light with thereflection phenomenon by, for example, changing the transmittance withreflectance.

1-65. (canceled)
 66. A pattern formation method using a photomask having a mask pattern formed on a transparent substrate and a transparent portion of said transparent substrate where said mask pattern is not formed, the pattern formation method comprising the steps of: (a) forming a resist film on a substrate; (b) irradiating said resist film with said exposing light through said photomask; and (c) forming a resist pattern by developing said resist film having been irradiated with said exposing light, wherein in said photomask, said mask pattern includes a main pattern to be transferred through exposure and an auxiliary pattern that diffracts exposing light and is not transferred through the exposure, said main pattern is composed of a first semi-shielding portion that has first transmittance for partially transmitting said exposing light and transmits said exposing light in an identical phase with respect to said transparent portion, and a phase shifter that transmits said exposing light in an opposite phase with respect to said transparent portion, said auxiliary pattern is made from a second semi-shielding portion that has second transmittance for partially transmitting said exposing light and transmits said exposing light in the identical phase with respect to said transparent portion, and a pattern width of said auxiliary pattern is smaller than that of said main pattern.
 67. The pattern formation method of claim 66, wherein in said photomask, said first transmittance is 15% or less.
 68. The pattern formation method of claim 66, wherein in said photomask, said second transmittance is not less than 6% and not more than 15%.
 69. The pattern formation method of claim 66, wherein in said photomask, said first semi-shielding portion and said second semi-shielding portion are formed by the same semi-shielding film.
 70. The pattern formation method of claim 68, wherein in said photomask, said first semi-shielding portion and said second semi-shielding portion are formed by the same semi-shielding film.
 71. The pattern formation method of claim 66, wherein in said photomask, said phase shifter is disposed at a center of said main pattern to be surrounded by said first semi-shielding portion.
 72. The pattern formation method of claim 71, wherein in said photomask, a dimension of a part of said first semi-shielding portion sandwiched between said phase shifter and said transparent portion is not less than 20 nm and not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 73. The pattern formation method of claim 71, wherein in said photomask, a dimension of a part of said first semi-shielding portion sandwiched between said phase shifter and said transparent portion is not less than ¼ of a wavelength of said exposing light and not more than (0.3×λ/NA)×M, wherein λ indicates the wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 74. The pattern formation method of claim 66, wherein in said photomask, said phase shifter is disposed in a peripheral portion of said main pattern to be surrounded by a part of said first semi-shielding portion.
 75. The pattern formation method of claim 66, wherein in said photomask, a part of said transparent portion is disposed between said main pattern and said auxiliary pattern, and with respect to an oblique incident angle φA defined as sin φA=NA×SA when a given oblique incident position is indicated by SA (wherein 0.4≦SA≦0.8), a center of said auxiliary pattern is disposed in or in the vicinity of a position away from a center of said main pattern by a distance M×λ/(2×sin φA)), wherein k indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 76. The pattern formation method of claim 66, wherein in said photomask, a part of said transparent portion is disposed between said main pattern and said auxiliary pattern, and with respect to an oblique incident angle φB defined as sin φB=NA×SB when a given oblique incident position is indicated by SB (0.4≦SB≦0.8), a center of said auxiliary pattern is disposed in or in the vicinity of a position away from a center of said main pattern by a distance M×((λ/(2×sin φB))+(λ/(NA+sin λB)), wherein λ indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 77. The pattern formation method of claim 66, wherein in said photomask, said auxiliary pattern includes a first auxiliary pattern that is disposed with a part of said transparent portion sandwiched between said main pattern and said first auxiliary pattern, and a second auxiliary pattern that is disposed on a side of said first auxiliary pattern farther from said main pattern with a part of said transparent portion sandwiched between said first auxiliary pattern and said second auxiliary pattern.
 78. The pattern formation method of claim 77, wherein in said photomask, when a given oblique incident position is indicated by SA (wherein 0.4≦SA≦0.8), with respect to an oblique incident angle ( φA defined as sin φA=NA×SA, a center of said first auxiliary pattern is disposed in or in the vicinity of a position away from a center of said main pattern by a distance X=M×(λ/(2×sin φA), wherein λ indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 79. The pattern formation method of claim 78, wherein in said photomask, with respect to an oblique incident angle φA defined as sin φA=NA×SA when a given oblique incident position is indicated by SA (0.4≦SA≦0.8), a center of said auxiliary pattern is disposed in or in the vicinity of a position away from a center of said main pattern by a distance M×((λ/(2×sin φA))+(λ/(NA+sin φA)), wherein λ indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 80. A pattern formation method using a photomask having a mask pattern formed on a transparent substrate and a transparent portion of said transparent substrate where said mask pattern is not formed, the pattern formation method comprising the steps of: (a) forming a resist film on a substrate; (b) irradiating said resist film with said exposing light through said photomask; and (c) forming a resist pattern by developing said resist film having been irradiated with said exposing light, wherein in said photomask, said mask pattern includes a main pattern to be transferred through exposure and an auxiliary pattern that diffracts exposing light and is not transferred through the exposure, said main pattern is composed of a first semi-shielding portion that has first transmittance for partially transmitting said exposing light and transmits said exposing light in an identical phase with respect to said transparent portion, and a phase shifter that transmits said exposing light in an opposite phase with respect to said transparent portion, said auxiliary pattern includes a first auxiliary pattern that has a width D1 and is disposed with a part of said transparent portion sandwiched between said main pattern and said first auxiliary pattern and a second auxiliary pattern that has a width D2 and is disposed on a side of said first auxiliary pattern farther from said main pattern with a part of said transparent portion sandwiched between said first auxiliary pattern and said second auxiliary pattern, and said width D2 is larger than said width D1.
 81. The pattern formation method of claim 80, wherein in said photomask, a ratio D2/D1 is not less than 1.2 and not more than
 2. 82. The pattern formation method of claim 80, wherein in said photomask, said phase shifter is disposed at a center of said main pattern to be surrounded by said first semi-shielding portion.
 83. The pattern formation method of claim 82, wherein in said photomask, a dimension of a part of said first semi-shielding portion sandwiched between said phase shifter and said transparent portion is not less than 20 nm and not more than (0.3×λ/NA)×M, wherein λ indicates a wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 84. The pattern formation method of claim 82, wherein in said photomask, a dimension of a part of said first semi-shielding portion sandwiched between said phase shifter and said transparent portion is not less than ¼ of a wavelength of said exposing light and not more than (0.3×λNA)×M, wherein λ indicates the wavelength of said exposing light and M and NA indicate magnification and numerical aperture of a reduction projection optical system of an aligner.
 85. The pattern formation method of claim 82, wherein in said photomask, said main pattern is composed of a shielding portion replaced with said first semi-shielding portion and said phase shifter.
 86. The pattern formation method of claim 80, wherein in said photomask, said phase shifter is disposed in a peripheral portion of said main pattern to be surrounded by a part of said first semi-shielding portion.
 87. The pattern formation method of claim 80, wherein in said photomask, said first semi-shielding portion has transmittance of 15% or less.
 88. The pattern formation method of claim 80, wherein in said photomask, said first auxiliary pattern and said second auxiliary pattern are made from a shielding portion or a second semi-shielding portion that has second transmittance for partially transmitting said exposing light and transmits said exposing light in an identical phase with respect to said transparent portion.
 89. The pattern formation method of claim 88, wherein in said photomask, the transmittance of said second semi-shielding portion is not less than 6% and not more than 50%.
 90. The pattern formation method of claim 66, wherein an oblique incident illumination method is employed in the step of (b).
 91. The pattern formation method of claim 66, wherein in the step of (b), said exposing light is emitted by annular illumination.
 92. The pattern formation method of claim 91, wherein an average of an outer diameter and an inner diameter of a lighting shape used in said annular illumination is not less than 0.58 and not more than 0.8, whereas values of said outer diameter and said inner diameter are standardized by numerical aperture of an aligner.
 93. The pattern formation method of claim 66, wherein in the step of (b), said exposing light is emitted by quadrupole illumination.
 94. The pattern formation method of claim 93, wherein a distance from a light source center to a center of each of four polarized lighting shapes used in said quadrupole illumination is not less than 0.4/(0.5)^(0.5) and not more than 0.6/(0.5)^(0.5), whereas a value of said distance is standardized by using numerical aperture of an aligner.
 95. The pattern formation method of claim 80, wherein an oblique incident illumination method is employed in the step of (b). 